Minetest may be a better comparison to Roblox here. Modding has first-class support and is a basic part of the game, everything can be serverside unlike Minecra

Minetest may be a better comparison to Roblox here. Modding has first-class support and is a basic part of the game, everything can be serverside unlike Minecraft where mods have to match up, Minetest's mods also use LUA like Roblox (and Garry's Mod). Bonus points, Minetest is free as in freedom software, so out of all these, I'd be most comfortable recommending it to someone.