Mumble - Mumble is an open source, low-latency, high quality voice chat software primarily intended for use...
Unity - The multiplatform game creation tools for everyone.
Discord - Step up your game with a modern voice & text chat app. Crystal clear voice, multiple server and channel support, mobile apps, and more.
Godot Engine - Feature-packed 2D and 3D open source game engine.
RaidCall - Free & Light. Setting up is fast and easy; with no need to rent or set up servers. Low CPU usage and minimum memory footprint allows for smooth, uninterrupted communication. im. Group Communication.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.