Some links to a great way of sharing tunes on the internet. There are thousands of tunes already there, and it is quite easy to learn how to use the (free) software:

ABC homepage – explains how it all works
Some of the available software – I use ABCexplorer
Use Mandolintab to convert your ABC text to music or tab
Convert your ABC text to XML to use in MuseScore
One possible start point for finding tune collections

Looking for a tune? Try the Session for (mainly) traditional tunes, with music, midi, ABC and discussions of the tunes