TranslationLinux also has some stuff that offers some features close to Main Stage and Gig Performer.
As far as I can tell these two together provide the nearest feature set, but are a bit rough and may not be stable enough for live use (although there are videos of it being used live that do work out fine.)
Carla
Carla is a fully-featured modular audio plugin host, with support for many audio drivers and plugin formats.
It has some nice features like transport control, automation of parameters via MIDI CC and remote control over OSC.
https://kx.studio/Applications:Carla
Konfyt
Konfyt is a digital keyboard workstation for Linux which allows the user to easily and quickly set up patches, each with multiple layers, and instantly switch between these patches for seamless live keyboard playing.
http://www.noedig.co.za/konfyt/
In general these searches are useful:
https://linuxmusicians.com/search.php?k ... +performer
https://linuxmusicians.com/search.php?k ... =cantabile
