Roblox is a game platform — but it has many, many games on it. They are largely made by the community, all thanks to the very permissive Lua programming language. You can find anything from fan-favorite horror titles like Doors (I reached 86th!) to World War I multiplayer shooters with digable trenches.
Players can wildly customize their character model, especially if they have the Robux (in-game currency purchased for real money) to splash. And yes, Roblox platform users can even make cosmetics!