Hampshire has a lot of people with varied interests, and it is very easy to start a club- 3 students as signers is all you need to get a budget for one year. The most popular groups include the two a cappella groups (a third all-female group has recently started), the two improv troupes, the incredibly talented Hampshire Circus, the Frisbee team (the Red Scare, and our only serious sport, although we have other teams that come and go- all sports are of the informal, anyone-can-join, intramural variety), and groups that organize some of the bigger events on campus- Drag Ball is run by the Queer Community Alliance (which is a pretty active group in general), Deathfest is a huge Dungeons & Dragons-based tournament (most of the characters and rules changed to reflect Hampshire culture) run by Mythos (they also organize weekly Capture the Flag games). There's a campus newspaper, the Climax, and there's a magazine, the Omen (it publishes anything submitted to it, and is thus frequently a point of great controversy). The Dean of Students has a knitting circle that is a Hampshire Institution. Most Hampshire groups, however, are short-lived, but there are always a lot to choose from, and, if no one's doing what you want, you can just grab two friends and start your own.
Hampshire housing tends to create a unique community as well- we have two buildings of traditional dorms, and the rest of the housing is in what we call mods- basically 4-10 person apartments, with a shared kitchen and common space. The dorms are mostly single rooms, which means that you are nearly guaranteed a single your first year. Most mods have one double room. Mods are usually filled with close friends, and mod culture and dorm culture are different. Students in the dorms eat in the dining hall and have more chance to see other students. Some students who live in the mods get more insular- rarely leaving their own mod or grouping of mods, and others spend a lot of time in other people's mods and hanging out with friends who aren't modmates. The mods are definitely the site of the most parties, and each of the 3 mod groupings has a different reputation- Prescott is known for hipsters, wild parties, and drugs. Greenwich is usually the home of 2nd and 3rd years, and often the quietest of the mods, although it attracts a wide range of people. Enfield is considered the most desirable housing, and often has mostly Div IIIs, who host a lot of parties early in the year, when their Div IIIs are still in infancy, and and at the very end of the year, when they've finally finished. In between, it's an area that fluctuates- never as wild as Prescott, but usually not as quiet as Greenwich. Each mod can differ greatly based on who is living in it, of course. The dorms are the domain of first and second-years almost exclusively, and the social scene reflects that- the dorms aren't usually the site of many parties, though.
Hampshire students have a lot of social options, in spite of the small size of the campus. If you don't want to party, it's not hard to find friends who are similarly more interested in quieter evenings. The Gamer Hall (another Hampshire institution) has at least 3 consoles going at almost any hour of the day or night, keeping its population busy. Hampshire students are inclined to have dinner parties, tea parties, board game nights, or any manner of other amusements. Just like in our academic life, we really have the opportunity to make our social life exactly what we want.
There are no fraternities or sororities on campus, and most Hampshire students like it that way. If you crave Greek parties for some reason or another, UMass has a pretty active Greek life- in fact, the 5 College community ensures that if, for some reason, nothing you want to do is going on at Hampshire, you can probably find it at one of the other schools.
Hampshire theater is one of the hugest "departments" at Hampshire, and there are always more shows a semester than there is space for- you could see a Hampshire-produced play every week if you wanted. The shows are usually pretty good, and there are also a ton of Hampshire students who are in bands, or do dance performances, or the like, in addition to the incredibly talented performing arts groups of the other colleges.
Hampshire has 2 really big events each year- Hampshire Halloween (legend by this point) and Drag Ball. Halloween is the kind of even that actually closes down campus- anyone who isn't a Hampshire student has to be personally invited by a Hampshire student to be there. Every band on campus performs, the circus performs, the belly-dance troupe performs. Every House has events, and the event is known for very prevalent drug and alcohol use, although it is definitely possible to enjoy it without substances. Drag Ball happens in the spring, and is also hugely popular- Hampshire students perform in drag (and we have some very talented drag kings and queens in our student body), almost everyone comes in costume, and proceeds to dance their hearts out while seeing how amazing or ridiculous everyone else they know has managed to look.