I am a fellow Linux user in the field of game development. I recently came across Indiegogo of Garage games for a port of their game engine Torque 3D to Ubuntu.
Torque 3D is open source under the MIT license you can find it on Github it is windows only at the moment however they do have a functioning Linux server for it.
They also announced that they will be open sourcing Torque 2D and iToruqe as one package also under the MIT license in the near future! I mention this as Torque 2d has the some of the same core systems as Torque 3D.
I hope that this is helpful to some!
Indiegogo - Link
Torque 2D MIT Announcement - Link
Torque 3d Github