Does it allow for HTML, CSS, JS to be used to make GUIs? Any place where I can see the limitations of the API? Is this as powerful as other MP mods out there?
Yes, NUI uses a Chromium window that can render any web page element.
Yes, as was answered above
Most, if not all, known natives in the GTA community are available. A list of all natives can be found here: https://runtime.fivem.net/doc/reference.html
You can use these natives easily inside Lua and C# code with camel caps
GET_VEHICLE_PED_IS_IN would be:
I don’t know what you mean by powerful, but it’s just as a sandbox environment, possibly even more than other MP frameworks. For example, FiveM has synced NPCs across clients whereas other frameworks mostly don’t.