So you really want to play a song, but unlike the singer of the original you've hit puberty and figuring out all the right chords to lower the key is just no fun. Don't want to pay to upgrade to "pro" on chordify, etc.?

Well, just copy/paste the chords/lyrics from any online song repository in here and voila, change the key from tenor high range to comfortable bass and any in between:
http://www.logue.net/

Has been very helpful when I want to play on the banjo in double C tuning. I just convert to the key of C and easy peezy, key of C-y.