Godot is a full 2D and 3D game engine with editor.
FRT is a Godot 3 "platform" targeting single board computers. In plain English, you can export a Godot game to most of them by using FRT binaries, as long as the game has been designed with the limitation of the hardware in mind.
The latest versions of Godot 3 come with official export templates for arm32 / arm64 architectures. Using the official export templates should be your first choice.
The main difference is that FRT uses SDL2 under the hood, so, if your distro uses something other than X11, you can try if FRT works better for you. KMS/DRM and FBDEV are sometimes used, but Wayland has become more and more popular, and it might be interesting to see if your game runs better without going through xwayland.
Download the custom FRT templates from Releases and export to arm32 / arm64 as usual, selecting the FRT binaries in the Custom Templates fields of the Options tab.
You can also export a pck / zip file and manually use the FRT template to run it. This has the advantage that you only need to upload the FRT binaries once.
Details vary depending on your target board, but the end result is usually (a script with) a command that looks something like this:
frt_3.6.1-1_arm64_release --main-pack MyGame.pck
FRT tracks the latest stable version of Godot 3. Older versions of FRT can still be found here:
https://sourceforge.net/projects/frt/files/
The easiest way to compile FRT is to use docker.
Download Dockerfile and create a new docker image.
Start a new container and run:
$ frt-pull
to clone (or pull) the right branches from https://github.com/efornara/godot3 and https://github.com/efornara/frt.
Then run:
$ frt-compile
to generate the templates.
The arm32 templates terminate with "Illegal instruction" on some older boards. The official templates behave the same way. See godotengine/godot#112189 for more info.
If you are running a recent distro (e.g. trixie-based armbian), as a stopgap you can try the armhf binaries from these experimental trixie builds.