Bitcoin Core

https://bitcoinmagazine.com/articles/bitcoin-core-released-what-s-new-1456241356

 

Bitcoin XT is a patch set on top of Bitcoin Core. It implements various changes which you can read about on the website:
XT uses the same data directories as Core so you can easily switch back and forth. You will keep and continue updating the same block chain.
Bitcoin XT downloads are code signed and are built reproducibly using gitian. If you use it please sign up to the announcement mailing list so you can be reminded of new versions.