paintutils.lua:38: attempt to call nil
I get this error after downloading and compiling source
All "GUIs"/"OSes" just crash immediately or after setup

Duplicate of #478: this was fixed in #441. Whilst there hasn't been a new release, you can download a development build.

I built it and it didn't work
I did gradlew build
I had to download All The Mods 3 and get the jar
I just checked and the dev build has a org folder in the jar and I don't know why it won't be there when I build it

LuaJ isn't packaged when using Gradle: you'll need to run ./deploy.sh (on a Linux/Mac sadly) in order for this to work. There's a PR to simplify it but it hasn't been merged yet.

Yep, it's a bit of a pain - there's a reason we run a download server :).

but if I modify it how can I send it to my friends?

whoops

is there a way to deploy it with the org folder

You could open the produced jar with an archive tool (7zip, etc...) and copy the org folder across. That should be sufficient.

thx