Trixel, make trixel art.
Latest version can be used for free @ http://www.glendc.com/trixel/.
This project is currently no longer maintained or worked on. Feel free to fork it and continue the project in case you are interested in doing so.
As the GUI is still crappy at this point, here are the controls currently functional:
The editor is still quite young and there is a lot to do. Feel free to contact me in case you want to start contributing to Trixel. Additionally you can also just comment on an issue that you want to resolve, or open an issue related to a bug or feature you want. Once you're finished you can open a pull request, so that the review-and-merge process can begin.