For the past twelve years the Adventure Game Studio engine has been the place to go to create classic style adventure games. Unfortunately it has also been very closed source so development has always been by one person being the dedicated coder Chris Jones.
As of late last week Chris Jones has announced that he hasn’t had a lot of time for AGS in recent months and has decided to release the engine under Artistic License 2.0. At this point only the IDE has been open sourced, but over time hopefully the actual core of the engine will open-sourced as well.
I must thank Chris Jones for making this decision as this will see the AGS engine grow much more quickly and hopefully on the Linux side of things we will see a Mono port of the IDE.
Check out the engine at http://www.bigbluecup.com.
UPDATE: Seems someone has already started making the linux port (well started to at least). Here is a screenshot.