Originally running in Byond and now running on modern software under the broader heading of Space Station 13 and 14 respectively. It’s completely free and runs on potato computers.
With origins as a college project Space Station 13 is a simulation of a work shift on a space station feating several departments with multiple jobs each like Engineering, Science, Security, Command, Service, Entertainment, and Medical. Everyone works together to keep the station running. You must eat and drink while working to maintain a healthy speed. But each round an antagonist or a dozen of them spawn as well, they may be an agent of the syndicate seeking to steal important items or kill targets using contraband items only they have access too.
The graphics are pixel paper dolls sliding around a top down map. You can pickup items and interact with the world and other players as well. The possibilities are REALLY limitless. You can make drugs, cocktails, food, shuttles, your own bar in the maintenance tunnels, improvised weapons, and more.
There are dozens of servers each running their own fork of the code and featuring unique rules and mechanics. One server may have alien races with their own languages, another will have physics, way back when there was a fallout server with a vault section and wasteland section of the map and a raider faction and a vault faction at war.
Cannot recommend this game enough, it’s going through a renaissance right now and is a BLAST to play. Check it out, it’s free.