Cosmos-sdk is the successor to basecoin, but it is not yet ready. All
development is happening on branches and there is no stable API yet.
Potential release maybe late September. Please watch this space for details,
but please don't build on it yet.
You can currently use https://github.com/tendermint/basecoin to build your abci
apps. Much of the business logic code can be ported over without too
much difficulty.