Announcing The BiRD, short for "Bitcoin Relational Database".

It is an alternative "medium-weight" Bitcoin client for Windows with the following main features:

Talks the native bitcoin protocol: connects to the normal Bitcoin network;
Maintains a pruned version of the blockchain: Mbytes instead of Gbytes of data because only "unspent" transactions are kept;
Stores data into a relational database (MySQL): abstraction of the blockchain into easy SQL queries to retrieve balances and transaction details;
Medium weight: storing ALL unspent transactions (in comparison to a 'light' node which would only store transactions of a specific wallet);
Open-source: C++ source files can be found at github and can be compiled using the free MS Visual Studio C++ Express.

Goal:
To provide an alternative, medium-weight client to developers of new Bitcoin applications with a simple interface based on a MySQL database.
Nevertheless, up-to-date data including unconfirmed transactions are available (to counteract any double spend attempts).

History:
First release v0.1.0 alfa

Current weak(er) points:

Connects to only 1 full Bitcoin client, so you have to trust that client;

More information can be found at the website UBiCard.org, including download of the compiled version and snapshots of the database at different block heights.
It will be part of a larger project including a smart card (for storing the private keys and sign transactions) and a GUI client managing the wallets, cards and payments.

Any feedback/questions is much appreciated.

Thilo von Braun