Adventure Game Studio (AGS) "allows you to create your own point-and-click adventure games, similar to the early 90's Sierra and Lucasarts adventures. It consists of an easy-to-use development environment, and run-time engine."
What this means is that you can basically make your own adventure game, akin to Leisure suit Larry, Monkey Island, Day of the tentacle, without having to program a single peace of code! Just supply the artwork, make up an idea for a story, and click away! Of course, if you want to go more advanced you can customize pretty much anything with the help of AGS's powerful script language! And all this is FREE?! Yes, sirree!
Adventure Game Studio website!