wxWidgets - wxWidgets: Cross-Platform GUI Library
OpenAL - OpenAL is a cross-platform 3D audio API appropriate for use with gaming applications and many other...
Electron - Build cross platform desktop apps with web technologies
Wwise - Game audio engine, designed to give artists more control and save programmers' time.
GTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.
Unity - The multiplatform game creation tools for everyone.