The demo is available at GitHub, requires using an unstable build (unless you're building yourself) and the use of `git lfs clone https://github.com/godotengine/tps-demo.git`.
Thanks to its Patreon project, Godot Engine makes about $8000 per month (nearly $96,000 per year - of course there are Patreon fees but there might be nonpublic donations/support as well), which allows it to be much more than a passion project. Godot is being legally represented by Software Freedom Conservancy (I recommend this fantastic podcast about it).
One thing that bugs me about Godot right now is their download page:
If C# is stable, why not include it by default?
If C# is unstable, why present it as an equal to the stable version?
Anyways, let's look forward to a stable 3.1 and much useful documentation. Documentation for modern game engines by the way means free-to-use sample projects with code you can understand.
There actually is one functional FPS tutorial with no sound at all and unpleasant controls but technically it seems fine:
It is part of the official documentation.
By the way, I'm collecting open source game(dev) Discord servers on the following server: https://discord.gg/usAHQdz . 14 so far. Let us know if you know of any missed ones!