Yeah GMod is a good comparison, but it’s more powerful and you can do a lot more stuff, even replace the player characters and UI elements other than one menu. They also have a lot more infrastructure like a marketplace (for both developer assets and avatar items). But it’s also more exploitative:

Investigative journalism YouTube channel People Make Games accused the platform of “exploiting” younger game developers by promising them large amounts of money from creating games, only to apply high revenue cuts and leaving creators with little to no income. They likened the platform’s business model to a company scrip.[149][150] After Roblox requested the channel to take down the video, People Make Games released several more accusations towards Roblox, focused on an alleged lack of oversight of developers and a method for people to address developer abuse, leading to child developers being exploited for labor on third-party platform’s. They also criticized the platform’s virtual economy, comparing the limited collectibles market to gambling.[69][155][156][157] It has also been accused by Hindenburg Research of artificially inflating its monthly active player count.[158]

Don’t. That place is a sexual cesspool.