Although everything I do is under the license Creative Commons Attribution Share-Alike, I’m starting to group my pixelarts works and release them in single files under the GPL.
Here the first and small release:
In summary: you can use them freely for open source or proprietary, games or prototypes, professionals or beginners developers, for study or for lucrative purposes, whatever you want. You don’t need even ask me for that, just use it (but I appreciate a reference). You can even modify them as long you also maintain the same freedom for the derivative work. For complete details, read the GPL or ask your questions in the commentaries.
If you are looking for a free, big and great tileset, look the wonderfull work of The Mana Word project (both code and art under GPL).
Soon I’ll group others pixel art drawings of others games I made in a single tileset file.
If you have a similar work in a compatible license we can make release of them togheter and create a big free tileset.