http://www.indieroyale.com/

http://www.indieroyale.com/blog/the-july-jubilee-bundle

Puzzle Agent and the Geneforge series are the only ones I know of, but PA is pretty fun and Geneforge is an RPG series with storytelling that rivals the epitome of RPG storytelling, Planescape: Torment.  The entire series can provide close to 200 hours of gameplay so I highly recommend that.