Gig Performer is described as 'Build and control your live music rig with Gig Performer to transform and elevate your live performing experience by gaining complete control over the sound of your instrument or voice' and is an app in the Audio & Music category. There are more than 25 alternatives to Gig Performer for a variety of platforms, including Windows, Mac, iPad, Linux and iPhone. The best alternative is GarageBand, which is free. Other great apps like Gig Performer are Carla (Free, Open Source), VSTHost (Free Personal, Open Source), Cantabile (Paid) and AudioMulch (Paid).
Welcome to the school of rock. A Mac-sized practice space. Your own recording studio. If you want to learn to play an instrument, write music, or record a song, GarageBand can help — whether you’re a rookie or a rock star.
Carla is an audio plugin host, with support for many audio drivers and plugin formats. It has some nice features like automation of parameters via MIDI CC (and send output back as MIDI too) and full OSC control.
NanoHost is not a synthesizer. It is a free, minimalist host application for Windows that can load VST-synths. Furthermore, it can act as a wrapper which converts VST-synthesizers into standalone applications.