Behind adding checkpoints (on the @Windmaster fork), nothing else has been done on the client since the official release.
Umm, I think there are somewhat more changes in my fork than just adding checkpoints.. See if you can get the original official release to compile on Windows, and if you succeed (without replacing all the scrypt-jane library source with a newer version altogether), also keep score on how many times you see unchanged "Novacoin" and "NVC" text plastered all over the original client. Or try to get an estimate of the network hash rate out of the original client, or find out the current N or Nfactor without looking up the time-vs-N table I generated (and everyone else reposted in various places).
Hey sairon or Joe_Bauers (with Joe being the only one who has ever contributed code to my version of the client), want to take over my Github repository (github.com/yacoin)? My enthusiasm for continuing development is decreasing, given the number of people that constantly send me private messages that the sky is falling if we don't immediately hard fork to change {insert random non-critical thing here that is different in YACoin than any other coin and/or doesn't work exactly how someone wants it to, or that we need to protect against hypothetical attacks that only exist in the sender's imagination due to misunderstandings of how the code works}. My favorite is all the PM's I get demanding we hard fork to change the difficulty calculation so after Nfactor++ events, average block time won't temporarily rise from 1 minute to 2 minutes for a few days while difficulty adjusts (oh no!).
I no longer hold any appreciable amount of YAC (well, other than a few thousand laying around somewhere) and haven't for quite a while.