I've been working on and off over the last few months on a really fun and interesting project called Grail by Droggl. It's an open-source engine for writing point-and-click adventure games.
I don't know if you've ever tried to find an engine for writing a 2D point-and-click adventure that's open-source and cross-platform, but they're hard to come by! Grail is going to fill that gap. It's exactly what I was looking for.
When I found it I was surprised with how nice and high-quality the demo looked. At the moment there're still some important features that haven't been implemented such as items and inventories, but the code is really clean and extensible and these features aren't far off.
The engine is written in C++ and uses SDL. The aim is to have a simple scripting interface for defining a game's scenes, characters, music, and story. It's being designed to be as flexible as possible, so the user interface and other things can be defined by the game creator in the Lua script. Further down the road there will be a GUI editor and tools.
There's a simple demo at the moment, and you can play around with the script to see how it works. You can compile Grail from the code over at the Github repo.