VSTi Host is an pplication that allows VST plugins to be used outside of larger host applications (like Cubase, Logic, etc.). It also allows for sequencers that may not have native support for VST plugins and/or instruments (like ProTools, Logic 6, Vision, Digital Performer, and Metro for example) to use them, as long as the sequencer supports the OMS-IAC bus (OS 9) or CoreMIDI (OS X).

VSTi Host allows for simultaneous use of a VST instrument (VSTi) and 4 VST effects. In addition, it also allows for either AIFF file playback or real-time audio input through the VST effects, via a separately controllable input bus. The audio output can be streamed out through the SoundManager, any ASIO-compliant hardware, DirectConnect, or ReWire in real time in OS 9, or through any CoreAudio compliant device in OS X, or even recorded to an AIFF file.

VSTi Host is perfect if you have an extra Mac that you'd like to put to use as a virtual synth and/or effects unit, or if your sequencer of choice doesn't support the VST plugins you'd like to use.