Choose your custom business app: bespoke software, SaaS, or ERP?
Use a custom business app to run a process that belongs to your company: schedule a service visit, track a case, coordinate a team, or connect several tools. Choose SaaS when your need follows a standard pattern, an ERP module when the process crosses your central management system, bespoke software when your rules set you apart, and a mobile app when your team works mainly in the field.
Do not choose a label before you describe the work. Map the journey, roles, data, integrations, and failure cases. You can then compare solutions that address the same need and assign one person to own each decision and maintenance.
Define your custom business app by the work it completes
Your organisation uses a business app to carry out a precise activity. You can keep it within one department or connect several teams. You can choose a web tool, local software, an ERP module, or a mobile app that exchanges data with your information system.
Start with a verb and a result: assign a room, prepare a flight file, document a procedure, approve a quote, or close a service visit. Then add the people involved, rules, and exceptions. This neutral definition keeps you from confusing your need with the first solution a supplier shows you.
Write one priority journey from start to finish. For example: "A manager assigns a mission, the operator carries it out, the client approves the result, and accounting retrieves the required details." If you plan a build, the mobile app requirements document shows you how to turn this journey into criteria your team can test.
Compare four answers to the same need
Bespoke software, SaaS, and ERP mainly describe how you obtain and run software. When you say "mobile", you describe a usage channel. Your mobile app can therefore belong to a bespoke product, extend a SaaS product, or connect to an ERP.
| Option | Choose it when | What you gain | What you need to check |
|---|---|---|---|
| Custom business app | Your process, roles, or integrations do not fit a standard product properly | You adapt the journey and architecture to your rules | Rights assignment, repository access, accounts, hosting, data, documentation, and maintenance |
| SaaS | Your need follows a common use case and you accept the provider's functional framework | You start using a service quickly while the provider hosts and maintains it | Export, reversibility, data location, processors, security, and service changes |
| ERP module | The process already touches the company's master records, purchasing, stock, finances, or customer relationships | You keep coordinated management in the central system | Configuration, access rights, migrations, integrations, ownership of the master record, and impact on other teams |
| Mobile app | Your team works in the field, sometimes with an unstable network, or relies on device capabilities | You bring the journey closer to the work context | Offline mode, synchronisation, device fleet, permissions, local security, and the system the app connects to |
France Num, a French government digital service, describes SaaS as software you access online while the provider hosts it on external servers. The same French government service presents the ERP as an integrated software package that coordinates several operational and financial functions. Use these definitions to understand the model, then check every concrete guarantee in your contract.
Check what you really control
When you choose bespoke software, you do not automatically control the code, hosting, or data. To keep that control, require a suitable contract, a precise assignment of rights, your own production accounts, and an architecture your team can take over. France's National Industrial Property Institute (INPI) explains that a commissioned software contract does not automatically grant rights to the client and distinguishes software that an employee creates as part of their duties. Ask a lawyer to draft or review the assignment if software ownership determines your business.
Ask for written answers to five questions: Who owns the code repository? Who administers the cloud? Who chooses the processors? How do you export the data? How does another team take over the product? A code copy alone does not give you real control if you own neither the keys nor the documentation and have no right to use the software.
With SaaS, you still control your business decisions and your GDPR obligations, even when the provider runs the platform. France's data protection authority (CNIL) requires the controller to govern its processor through a written contract and check its safeguards. Examine the processing clauses, the processor chain, transfers, data return, and data deletion.
Adapt the choice to your sector
Scope an aesthetic medicine journey
Fictional example: A clinic wants to bring together a schedule, a preliminary questionnaire, photographs, and follow-up. SaaS can handle booking. An ERP module can take over invoicing. Bespoke software becomes relevant when the team must orchestrate clinical rules, separate consents, and a record that connects to several systems.
Do not turn a digital journey into a medical decision. Ask healthcare professionals to validate the clinical content, and work with your DPO, RSSI, and a lawyer on the processing. If a provider hosts personal health data for you that your team collects during prevention, diagnosis, care, or follow-up activities, check the scope of HDS (health data hosting) certification with the French national health digital agency, Agence du Numérique en Santé (ANS). Ask a qualified lawyer to determine the obligation in your exact context.
Orchestrate a luxury hospitality service
Fictional example: A hotel wants to pass a client preference from booking to room service without multiplying messages. The ERP or PMS keeps the master record. Staff can follow a precise journey in a business app, apply access rights by role, and send useful events back to the central system.
Define the master data before you design the interface. Name who can read, correct, and delete each piece of information. Do not copy all the data into every tool, because your team will then have to resolve discrepancies and apply retention rules in several places.
Coordinate a private aviation operation
Fictional example: An operator wants to coordinate the crew, aircraft, ground service, and late changes. An ERP can manage resources and purchasing. In a custom mobile app, the field team can view a mission, report a discrepancy, and resume synchronisation after an outage.
Ask qualified aviation professionals to validate every operational rule and safety procedure. Let those professionals keep the decision and use the software to apply the procedures they have approved. Never let the software invent an authorisation, qualification, or regulatory constraint.
Map your integrations before you choose
List every system the app reads from or changes: ERP, CRM, directory, payment, calendar, storage, or sector specific tool. For each one, name the internal owner, the master data, the synchronisation direction, the frequency, the authentication method, and the expected behaviour when the service stops responding.
Test the cases that break a neat diagram: a duplicate, a concurrent update, data that an operator deletes, access that an administrator removes, an unstable network, and an unavailable API. To make each integration reliable, also require usable logs and a recovery procedure. You can price this work more accurately with the method in the guide to the cost of a mobile app in 2026.
Protect data from the scoping stage
Start with the purpose of each piece of personal data. Reduce collection, assign access rights by role, set a retention period, then test export and deletion. France's data protection authority (CNIL) asks teams to minimise data and permissions, set security objectives in contracts, and maintain protection throughout the app's life cycle.
Add a risk analysis that covers accounts, devices, APIs, backups, and providers. France's national cybersecurity agency (ANSSI) advises granting the minimum privileges and making regular backups on separate media. Test the restore process. If your team cannot restore the data, you have not protected your continuity.
If your processing creates a high risk for people, check with your DPO whether you need to conduct an impact assessment. France's data protection authority (CNIL) details the criteria that trigger this assessment, including sensitive data, large scale, vulnerable people, and certain data combinations.
Budget maintenance without applying a magic percentage
You cannot derive a reliable monthly cost from the development price alone. Instead, calculate the capacity you need to fix, update, test, and publish. Add hosting, licences, monitoring, support, and backups. The number of platforms, integrations, data sensitivity, and service criticality change the scenario.
Separate three budgets: corrective maintenance for incidents, preventive maintenance for dependencies and security, and functional changes for new needs. This separation shows you whether the team protects the product or funds a new version. Use the guide to mobile app maintenance to build the schedule and budget around your constraints.
Ask the provider who monitors alerts, how quickly they qualify an incident, which environments they maintain, and how they prepare a recovery. For SaaS or ERP, the provider often includes the shared foundation in the subscription, but your team still manages configuration, access, integrations, internal support, and process changes.
Choose your provider based on evidence
Give every candidate the same priority journey. Ask each one for a response that separates facts, assumptions, options, and exclusions. Then check the deliverables: acceptance criteria, architecture, code repository, mock-ups, accounts, service inventory, documentation, tests, security plan, deployment procedure, and maintenance terms.
Also ask for an exit scenario. You need to know how you will retrieve the code, data, and access, how long the provider will support you, and what your team can no longer use without the provider. Ask qualified professionals to review legal commitments and data clauses when the project affects your continuity, sensitive data, or a regulated activity.
Answer frequently asked questions
What is a business app?
Your organisation uses a business app to run a precise process with its own roles, data, and rules. You can run it on the web, on a computer, or on a mobile device, and connect it to an ERP and other services.
Should you build it as custom software?
No. Choose bespoke software when your process sets you apart, when workarounds for a standard tool cost too much, or when your integrations require a specific architecture. Choose SaaS or an ERP module when its rules genuinely cover your need and its control terms suit you.
How much does it cost to maintain?
No universal amount or percentage can answer this question honestly. Build a monthly budget around team capacity, infrastructure, licences, support, and security. Adjust it for platforms, integrations, change frequency, and the impact of an outage.