How do I use them though? It doesnt seem to let me download and install any of them!
I see a lot of people posting custom eclipse engines...
You just need to download the engine, extract it, install the runtimes, run the server, and run the client.
Most engines on the site are no longer supported by the developer that made them, and many also don’t have working download links. I have several decent engines linked in my signature you can download.