There was no [ANN] for this, so I figured I'd throw it up for you guys.

As with the other "2nd gens," this is not a fork but rather a complete rewrite of all the foundational code.  It does however use some commonalities, for instance the C++ implementation includes usage of leveldb and boost.

http://ethereum.org/

Whitepaper
Source code repository
Forums

Features:
- Novel "memory-hard" hashing algorithm specification
- Use of GHOST blocktrees instead of a traditional blockchain for PoW data propagation
- Use of Patricia trees in block data structures
- Transactions which contain loop-enabled programmable instructions for the creation of novel derivatives and functions within the blocktree; these are deemed "contracts"
- New fees algorithm which adjusts based on several different parameters
- New difficulty adjustment algorithm
- Data in objects is encoded in recursive length prefix (RLP) notation
- Crowdfunding model

The author is Vitalik Buterin, among others.

Vitalik and co., contact me if you plan to make an official ANN here and I'll close this thread.

Please note:
This is not MC2 and I am not involved in its development, but I am closely watching this to see where it goes!