Apps similar to Rack Performer include Carla, which is free and open source. Other options are Giada, AudioMulch, Luppp and Kushview Element. You can choose from more than 10 Music Production Apps like Rack Performer for Windows, Mac, Linux and iPad.
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.
Giada is a free, minimal, hardcore audio tool for DJs, live performers and electronic musicians. Just pick up your channel, fill it with samples or MIDI events and start the show by using this tiny piece of software as a loop machine, drum machine, sequencer, live sampler or yet...
Italy
EU
AudioMulch is an interactive musician's environment for PC and Mac. It is used for live electronic music performance, composition and sound design.
Australia
Luppp is a music creation tool, intended for live use. The focus is on real time processing and a fast, intuitive workflow. With extensive MIDI mapping support, you can get looping just how you like!
IrelandEU
Element is a cross-platform, modular AU/VST audio plugin host. Create powerful effects racks and instruments by connecting plugins to one another. Load graphs on the fly for quick access to your sounds.
United States
AustriaEU
A VST (plus AudioUnit on OSX) plugin host designed for live use. Based on the JUCE 'audio plugin host' code, heavily modified to better suit my purposes.
Cantabile is a music workstation for live performing musicians. Build your ideal rig - one that leaves you free to focus on giving your best performance.
Plogue Bidule is a modular audio software with full VST, Audio Unit and Rewire support.
Canada
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.
GermanyEU
Live, modular sound design environment that enables a user to combine, split, layer and chain their VST instruments and FX.
United Kingdom
Blue Cat's PatchWork is a universal plug-ins patchbay that can host up to 64 VST, VST3, Audio Unit or built-in plug-ins into any Digital Audio Workstation (DAW) in one instance.
