thinking about a town simulation, you'd have to use a big saving file for the city, containing all houses, environment, progress etc. , a savegame file for every user, a script that handles all time-based operations (e.g. building a house would take 2 hours) that processes all request-scripts. you wouldn't need _that_ much php... but i really doubt it'd be fun. in my eyes, browser games live from the fact that you can play them anywhere, anytime, without havin to install anything special.