OpenERP is a free software. OpenERP and all its modules are released under the open source AGPL licence. You can download and use it freely without any restrictions, with an unlimited number of users.

The apps platform of OpenERP offer maintenance services to help companies running OpenERP without problems, directly accessible through the "Settings/Modules" menu:

• Upgrade to future versions (to benefit from new features)
• Update automatically for security and bugfix releases
• Maintenance service (unlimited bugfix guarantee)
• Optional Hosting (to use online)
• Installation of apps (community or official in one click).

The apps platform is not free, it costs $39/user per month for all these services. This source of revenue helps developing OpenERP to make it better versions after versions.

As OpenERP is open source, these services are optional. You can still install modules yourself (manually downloading from launchpad), update your instance to apply security fixes, fix issues you encounter or upgrade versions (which is much more complex).

In these services, the installation of new apps is free if you have less than 3 users. If you have more than 3 users, you have to do it manually or subscribe to the OpenERP Enterprise service.

If you installed the Linux sources, the 240 official modules are installed by default. So, OpenERP does not require to access the Apps platform for official modules. (it is required to install community modules). The windows auto-installer has the minimum number of modules required installed by default. Others modules are installed on demand.

We say that OpenERP is free because you are free to:

• spend time and do everything yourself manually, or
• spend money and benefit from OpenERP Enterprise services (one-click install, updates and upgrades) and/or partner services for the deployment

The details of all OpenERP Enterprise services are described here: http://openerp.com/pricing