It's an emulator! That plays old LucasArts adventure games, along with a handful of other similar titles. You'll still need the actual disks/CD, of course. Unless you want to play Beneath a Steel Sky, because Revolution Software provided the source code. Oh, and Beneath a Steel Sky is available as a free download from the site. The emulator also supports Simon the Sorceror 1 & 2, Broken Sword, and Flight of the Amazon Queen, which is also freely available thanks to John Passfield and Steven Stamatiadis.
Another thing is that the game is just so OLD (it came out in what, 98-99?) that it's not gonna appeal too well to people trying to get into the series. For instance, I went back and bought Half-Life (for 10 bucks)