Crayta is a game creation system that comes free with Stadia Pro. It's very similar to other game creation tools like Gary's Mod and Roblox, but what sets it apart is its exceptional ease of use. Worlds are created from voxels which, of course, might put some people off. However it's a worthy trade off when you realise how easily people can create their stuff. Everyone who ever played Minecraft can be a level designer in Crayta.
On the other end of the game development skill spectrum it features a full Lua code editor in-game. If you ever worked with Unity 3D you'll feel right at home in Crayta's advanced mode. You can truly make some very advanced games in this.
It's the first game to feature Stadia's State Share feature, which means you can get people to play your creations just by having them click a single link.
Unit 2 Games are in this for the long run. On the Crayta Developer Portal you can vote on which new features you'd like them to work on first. They also hinted they are already working on several features like Asset importing, vehicles and NPCs. It will be very interesting to see how much this product grows in the coming years.