TowerDefense is, you guessed it, a simple tower defense game. Given that is has programmer-art and programmer-sound, it's a bit of an ugly duckling. However, it was quite useful as a tool for me to learn more about the structure of a game engine and some of the basic services it provides. Everything from the levels you select from to the stats of the enemies and weapons are defined in text files, so I hope people have fun playing around with it and trying their hand at making their own levels.
You can grab the game here: TowerDefense.zip
It includes documentation about how all the configuration files work, but you can also read them here.
Technical stuff: This is a pretty simple engine that relies on Allegro for rendering. It does basic things like having a timed game loop and an object-hierarchy based on the Actor model that covers all the objects in the game world. It also provides some more (relatively) advanced functionality such as a resource manager that allows safe loading of different types of resource by name and sound pools to allow the same sound effect to be played several times simultaneously (something Allegro doesn't support well natively). None of this is really new or groundbreaking stuff, but it provided me a great sandbox to learn in.
If you have any questions (technical or otherwise), feel free to email me.