Panda3D is a powerful 3-D rendering engine for many Unix-based and Windows platforms. See the Panda3D home page at https://www.panda3d.org for more information and for forums and downloads. The source code is no longer hosted at SourceForge, but is now available from GitHub:
Panda3D is one of the best free engines you can find online to develop games. You have audio, physics, AI, network, shader support, packaging, installers, etc. all available to you. And while the engine is made in c++. You can code your game with Python only, so you have a very good language to just focus on one aspect: Developing your game. The documentation is great, the samples are good, and the community is very friendly and responsive.