Frogatto is a GPL code, proprietary-art game that has gone through a few revisions of tile art.  Since we're fans of open source (myself being the art director over at www.wesnoth.org), we thought we'd release some of our deprecated tiie art as open-source, since we ourselves aren't ever going to use it in our game.  We're reserving the rights to significant, "difficult to duplicate" parts of the latest content because we're trying to sell the game on the iPhone store.

If you want code to easily build a 2d game from this, we have it.  Check us out at www.frogatto.com, or chat with us at #frogatto on irc.freenode.net

Anyhow, these are 16x16 tiles for a platformer title.  There are six core tilesets here, along with several accessories/decorations.  The faded tiles that look like they've been alpha-blended with purple are meant to be background tiles.  Most of the others are self-explanatory, or subject to creative use.  Enjoy.