The Sims 2: Apartment Life is an expansion pack for The Sims 2, in which your Sims can now live in multi-unit rental properties, with multiple families per structure.
Once you've chosen your building, you can knock on your neighbours' door for socializing, find a roommate, pay your rent, etc.. Your landlord can even poke his head inside from time to time to see if everything is well. Also, this expansion pack features a reputation meter, indicating if you're received well by the community or not.