Both professional and volunteer developers contribute to Mesa.
Some of the companies that has made significant contributions include (sorted alphabetically):
The following companies can be contacted for custom Mesa / 3D graphics development (sorted alphabetically):
Volunteers have made significant contributions to all parts of Mesa, including complete device drivers.
There’s really too many to mention here, and the list keeps on changing but you can see an up-to-date list of significant contributors on our GitLab here.