Free software is not software that costs nothing. It is software you are allowed to read, change and pass on. On an ERP, which is where your bills of materials, your routings and your customers live, that difference decides how much room you have to move.
The Free Software Foundation Europe explains the idea better than we could, in under three minutes:
Plays from YouTube. The video is by the Free Software Foundation Europe, CC BY.
Four freedoms, and what they mean in a factory
The definition comes down to four things you are allowed to do: run the program for any purpose, study how it works and change it, pass copies to other people, and pass on the versions you have changed. Nothing about price. Plenty of free software is paid for, and plenty of software that costs nothing is not free at all.
On a management system those four turn into something concrete. If you can read the code, you can find out what it does with your data instead of trusting a brochure. If you can change it, the software bends to how you produce rather than the other way round. And if you can pass it on, the day you want to change supplier you take your work with you.
Why it matters more on an ERP than elsewhere
A photo editor you can replace on a Tuesday afternoon. A management system holds ten years of orders, part numbers, costs and customers, and it is wired into how everybody in the company works. Replacing it is a project, not an afternoon.
That is exactly why the question of who owns the code is not academic. A closed system is a room with one door, and somebody else keeps the key. It might be a perfectly good room. But you should know the shape of it before you move the furniture in.
Where we stand
We work only on the Community edition of Odoo, which is free software. The modules we write go out on the Odoo App Store under AGPL, which obliges anybody who takes them to keep them open as well. What we build for a customer, that customer can read, keep and take away.
It is not generosity. It is the arrangement we would want if we were on the other side of the table.
There is more on how we work, and the two associations we belong to, on the open source page.