Roblox didn't have server functions until 2014 and they weren't mandatory until 2018. Anything the client did automatically replicated to every other client.

That meant I could attach Cheat Engine to Roblox, edit memory addresses to give myself in-game cash, and inject whatever code I wanted to everyone else.

Thankfully it was sandboxed so I couldn't give people viruses.

This was probably a good decision because most of Roblox's best games from that period weren't updated to use server functions. It's too difficult.