"Prophunt" is a name players of many different games will know. From Team Fortress 2 to Counter-Strike, most any Source Engine game supports some kind of Prophunt game mode. But this particular title – "Garry's Mod - PropHunt Hide'n'Seek - Original" in full – is the first instance of the game. It features several advantages and disadvantages over other ways of playing Prophunt, but most importantly, it's free if you already have the base program, Garry's Mod.
Hunter and the hunted
In Prophunt, two teams square off on the field of "battle". One team, the red team, chooses from an array of props to appear as. Then they attempt to blend in with the map they are playing on, while the blue team, armed to the teeth, attempts to seek and destroy these cleverly-disguised props. There's a huge array of props, and maps to go with them, which is important as both props and maps are usually pooled from other Source games: a sign from Team Fortress 2 might stick out like a sore thumb in a map from Counter-Strike: Global Offensive! When the round is over, either through the props' survival or their destruction, the teams change, and the game begins anew.
There's props wherever you go
Garry's Mod - PropHunt Hide'n'Seek - Original is based on Garry's Mod, just as the name implies. Garry's Mod, of course, is a sandbox of sorts where a player can move around and mess with assets from any Source game they can think of. It includes a huge bevy of tools to make for wacky situations and beautiful creations alike, and Prophunt is just one of many things you can do with it. Although Prophunt doesn't let you fling 30 trailers, stuck together, into the air and detonate them, it does let you use all of the same Source engine assets that Garry's Mod does. The "props" which the red team turn into can be pooled from any of these games, as long as the server you're on permits it. Since anyone can host their own Garry's Mod Server, and Prophunt servers are in short supply normally, it's easier than it sounds to round up a few players and mess with props from any game you want. Prophunt is even compatible with many other Garry's Mod extensions, although some will explicit not work.
To sum up
Garry's Mod - PropHunt Hide'n'Seek - Original is well worth trying if you already have Garry's Mod, and maybe worth getting it for if you don't. The game features the same sort of team-based gameplay anyone who's played a Source game knows, with a wacky, fun and less violent twist. Although the game is somewhat rough around the edges in the way it is coded, it's important to remember it was made independently.