For the last few years I've been working on Gigalomania ( http://homepage.ntlworld.com/mark.harman/comp_gigalomania.html ), which is a Mega Lo Mania clone - some of you may remember the game from the early '90s. For those that don't, it's a simple 2D RTS game where you can advance through the ages.
It's available for Windows, Linux, OS X, Android and more.
Lots of the graphics are sourced from Open Game Art - see http://homepage.ntlworld.com/mark.harman/comp_gigalomania.html#licences for a full list.
If anyone wants to help out with improved graphics, that would be greatly appreciated. Areas of improvement still needed include: the buildings (which are rather simple 3D models and lack variation); defenders (mostly unanimated and rather simple looking); overall lack of consistency.