If you are referring to the "last beta", then it's just what it says on the tin - it's the last of beta releases, meaning that it's unsupported and it's the end of the line, feature-frozen since mid May, no updates. The exact list of differences is over at [1]. The reason the last beta exists is that the beta period was quite long and there were people who got used to using the app for free, so that version is for them (though all beta users got 50% the production version).
[1] http://www.donationcoder.com/forum/index.php?topic=36388.msg...