http://obsidianconflict.com/about.htmlThis mod is probably most comparable to Synergy. I'm not sure if it's the exact same style, but it's pretty cool.
For example; one map starts out with you in a weird black room, and guns all over the floor. You pick them up, and walk into the center of the room, which is glowing blue. Once inside, you will be teleported in a house. In the house is a basement, and normal rooms you'd see in a house (laundry room, bathroom, closet, bedroom, etc.). There's also a work shack outside with a chainsaw, and a few saw blades.
I won't spoil much, but you need to activate something in order to trigger something...
It's a very intense map. Very fun to block up the doors with sofas and dryers. If you lose the living room, it's best to stay in the bedroom, since there is a nice spawn of shotgun ammo in the closet, and there's a mattress and bed frame there to block off the two doors.
Another popular map is the fishing maps. I can't really remember their names, but I'd remember them if I saw them.
In the fishing maps, you start out on this dock. There are many fishing poles along the edges of the dock, and a baskets that respawn watermelons. You use your gravity gun to put the watermelons on the fishing hook, and dip it in the water. Random items will appear at random times. Once you have something on your hook, you must pull it up on the dock, and take it off the hook. The hard part about this is that the item will spawn randomly around your hook, not very often that you will be able to get it, since it despawns after a few seconds.
The fun part about this map is trying to find the rare stuff. There are many rare things to find, and all of them are really fun to play with if you have a lot of people on the server.
One rare item is a giant wooden platform that, with a little effort from the people with you, you can use your gravity gun to push it over to the island that's really far away.
Something you should know before going into the water of the fishing maps, do not go in the water to try to steal the stuff from someone else's hook. In earlier versions of the map, the water had a seal on the surface that would allow you to go into, but not come back up unless you're climbing on a ladder to get up. In the later levels, I think I remember them putting leeches in the water.