GEM (Graphics Environment for Multimedia) is a library for 
Pure Data. 

Pure Data (or just "Pd") is an open source visual 
programming language for multimedia focused on computer 
music. 

GEM is really a bridge between Pure Data and Open GL. 

Although GEM could feel limited for programming visuals
it's deeply connected to Pure Data which is in turn 
is highly musical in nature. 

Some strong point about GEM: 

 - Visual programing language
 - Live coding (no compiling)
 - Strongly integrated to audio
 - Midi integration
 - Open source and well supported
   on linux
 - Although visual, code is saved 
   in easy to manipulate txt files

Recently a new library has been added to Pure Data called 
Ofelia, which is a bridge from Pure Data to Open Framework 
and Lua. It extend the visual possibilities, somewhat 
a replacement for GEM. 

https://github.com/cuinjune/Ofelia


The discord channel for Pure Data is really
active and makes it really enjoyable. 

https://discord.gg/DKG98HQp

Suiteru, using his Model:Cycle to control a GEM patch made
me fall back in love with Pure Data. He really got me back
into GEM and creative coding in general!

https://www.youtube.com/@suiteru


The commercial version of Pure Data, Max MSP: 

https://cycling74.com/products/max


__________________________ Other multimedia language


(FLUXUS)

My first live coding visual creating tool. 
It's a very powerful code, but the user base
seems pretty small so not easy to learn. 

https://www.pawfal.org

PROCESSING

I've spent a lot of time in Processing. Coding synth
visuals and games. 

https://processing.org

VVVV

Only running on windows, very powerful but I haven't had
a chance to play too much with it. I had the pleasure to
party with the vvvv crew back in Berlin many years ago

https://vvvv.org


CINDER++

I've seen a few different project built in Cinder++ 
https://www.libcinder.org

OPEN FRAMEWORK

A C++ library for building multimedia project. With 
the OFelia project, this library can now be used
with Pure Data

https://openframeworks.cc