Steinberg ASIO multi

ASIO (Audio Streaming Input Output) is a technology of Steinberg. It allows for low latencies and pretty much every state-of-the-art audio device is nowadays delivered with an ASIO driver (on Windows, at least). However, the basic idea behind ASIO is that professional audio applications entirely take ownership of the ASIO device.
Only very few ASIO drivers support true multiple application access. This effectively means that you can not use 2 or more applications using the same ASIO device at the same time.
The ASIO Multiclient wrapper overcomes this problem by providing a 'proxy' ASIO driver (the ASIO client), several of which can connect to the one ASIO Server, which in turn 'speaks' to the target ASIO device (driver). The server mixes the output streams of all applications, and provides that mix to the target device.