It’s a VST-compatible host that’s capable of:

• loading VST effects (aka “plugins”)
• parameterizing / editing them
• sound output for VSTis
• MIDI-input and -output
• loading / saving .fxb / .fxp files
• I/O through either Windows MME or ASIO drivers
• Wave Player / Recorder
• MIDI Player

While the program started mainly as an aid in understanding and debugging VST plugins, it has evolved into a quite capable program by now which can be really helpful in a keyboard artist’s Live setup.

www.hermannseib.com/english/vsthost.htm