From Hydrogenaudio Knowledgebase
ALSA or Advanced Linux Sound Architecture is a project, which seeks to provide MIDI functionality to the Linux operating system. ALSA has the following significant features.
- Effcient support for all soundcards from consumer to professional multichannel audio devices
- Fully modularized sound drivers
- SMP and thread-safe design
- alsa-lib in order to simplify the high level API
- Support for the older OSS API.
 ALSA over OSS
There are many advantages ALSA has over the older (but perhaps not the newer) OSS API:
- multi-thread safe design
- transparent use of plugin architecture to handle format,rate,channel cnt and many other conversions
- support for non-interleaved interfaces
- user-space software mixing (dmix)
- user-space "loopback/snoop" capabilities
- merging multiple cards into a single virtual device
- hiding non-ALSA-drivers behind a consistent user-space API (e.g. IEEE1394 drivers, or JACK)
- consistent and generic control API for managing hardware controls
- Flexible mixer architecture to handle modern audio interfaces fully (rather than reducing them to a simplistic device)
- consistent support for multiple instances of the same card
- linked operations of multiple cards
 Development API
 ALSA Library API
 ALSA Documentation
- ALSA wiki a large wiki pertaining to major ALSA related topics.