Awesome

qfusion

http://qfusion.github.io/qfusion/

qfusion is the id Tech 2 derived game engine

Features (incomplete list)

Fully open-source under the GPLv2 and easy to mod
Runs on Linux, macOS, Windows and Android (in development)
Modern and fast OpenGL 3.0 and OpenGL ES 3.0 renderer, running in a dedicated program thread
Realtime lighting and shadows via omnidirectional and cascaded shadow maps
Scriptable <a href="https://github.com/Qfusion/qfusion/wiki">User Interface</a> based on XHTML/CSS standards with support for remote content and scalable vector graphics
Support for vertex and skeletal animation
HDR & Bloom support with configurable color correction profiles
Fullscreen Anti-Aliasing support in the form of MSAA or FXAA
Powerful multiplayer & eSports features (global stats, friend lists, IRC, TV-server, etc.)
Ready to go FPS example gametype scripts from Warsow
Multithreaded sound mixer design
OpenAL support
Hardware-accelerated Ogg Theora video playback

Extensible

C/C++ mods (plugins) can ship new gameplay features while maintaining compatibility with the core
UI and game mechanics scriptable with <a href="http://www.angelcode.com/angelscript/">AngelScript</a> (C++ style syntax)
Flexible HUD scripting
"Pure" (models, maps, textures, sounds) game content is automatically delivered to players by game servers
Players are allowed to locally override non-"pure" game content

Notable games

<a href="https://www.warsow.net/">Warsow</a>

License (GPLv2)

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.