Airsoft guns are model guns that use compressed air to fire a small rubber or plastic pellet. These pellets are usually around 5mm-6mm, and muzzle velocities around 60m/s aren't surprising.
Some of these guns are replicas of real guns, while some are completely, entirely fake.
The first airsoft guns used spring-loaded plungers to force air out of a chamber and drive the pellet down the barrel. Then came pump guns similar to American BB guns, where some lever is cycled to pressurize a chamber. Then there were guns that used regular compressed air to drive the pellet, and then compressed freon.
At this point, California passed a law outlawing the guns, not because they used freon, but because they looked too realistic, and people were getting killed by cops.
Airsoft guns then went back to compressed air, though I understand there are still freon models around. Recently I've seen battery operated airsoft guns. I haven't gotten ahold of one to take apart, but presumably the battery runs a small low-pressure compressor. I don't have any idea how long the battery lasts, or how well these guns fire.
When I first got into airsoft guns, every one of them was single action: cock gun, fire gun, cock gun, fire gun. By the time I stopped they were coming out with some fully automatic guns, but their air tanks froze up too quickly to be reasonable.
Some people just collected the things. There was quite a collector's market for them. But most of us would stage fights with them. My group had the advantage of being local to 5000 forested semi-private acres (the woods behind UC Santa Cruz) and a friendly police force. So we'd run around the woods shooting at each other.
Our most popular game was a variant on capture the flag. We'd split into two teams, and one team would stash a flag (usually a shirt or something) somewhere in the woods. Now those woods had quite a few crannies, so we made them put the flag somewhere where it would be clearly visible from a reasonable distance (like 50 ft). Then the other team would try to get to the flag. Anyone who got shot was out for 5 minutes, at which point they could come back in. The game went on until the flag was captured or we decided to call it.
My personal favorite was played in a weird grove of elm trees. There was a large clearing, about 100ft diameter, but oblong. In the middle of the clearing was one elm tree, and all around the clearing was nothing but elm trees and lots of leaves on the ground. These trees were very thin (about 6-12 inches diameter) and stood straight up. The lowest branches were about 12 feet off the ground. So effectively it was an area with just poles that didn't really provide effective cover. We'd leave all our stuff (including our guns) at the base of the tree in the middle of the clearing, and then spread out along the outside of the clearing. On some signal we'd rush in, grab the bare minimum of stuff, and run out while loading the gun and trying to cover out retreat. Then it was every man for himself. And if you ran out of gas or ammo, or your gun broke, you had to brave the clearing again to get more supplies. Great fun and very tiring.
We had another every-man-for-himself game that we played really deep in the woods. There was a very wide gully (about 200 yards wide) with a moderate to steep slope. There were lots of thickets and trees growing on this slope, especially some wonderful sniper positions from within rotten trees and under fallen trees and such. We'd play a simple war on the slope there. Everyone shoots at everyone. Lot's of fun.
When my friend or I organized these games, we always made a point of calling the campus police first and inviting them to join us (they never took us up on the offer). But that at least warned them that they might get calls about gun toting maniacs running around the woods. But one time someone else organized the game and didn't call ahead. Surprise, surprise, when we came out of the woods, there were lots of very nervous SWAT (100% of UCSC's campus police are SWAT) waiting for us. We let them take photos of the guns, and everyone was happy.
Haven't played recently, mostly because I've been too busy.
I've recently been told of some airsoft distributors who still do business in the US. Here's the only one I've checked up on so far:
This next link will take you to someone who has set up an airsoft discussion board. I avoid it because he uses frames and blink, but that's personal taste. I haven't read any of the board yet, for reasons that should already be obvious.