If you want to step (deeper) into modular synthesis, Omri Cohen is one of the best teachers for that on YouTube. If you should not know, VCV Rack is a free software version for modular synthesis and there’s an iOS port available called MiRack.
Gleetchlab is a modular performance DAW dedicated to glitch and experiemental music (20 Euro).
FamiStudio is a free simple, DAW-style, music editor for the Nintendo Entertainment System. It is designed for both chiptune enthusiasts and the NES homebrew community.
MPC Beats, the fully featured, beat-making software based on the legendary MPC workflow to quickly make great sounding beats.
Download MPC software for free at AKAI. It is a fully featured, beat-making software based on the legendary MPC workflow to quickly make great sounding beats.
Caustic 3 is a music creation tool inspired by rack-mount synthesizers / samplers rigs. Everything is real-time and optimized for mobile devices.
But the desktop version is free (No support)
Soundbridge is a free DAW featuring all you need to produce full songs like sequencer, mixer, sample editor, many FX, drum machine and such.
Giada is a free sequencer environment for handling your samples and loops. VSTs can be loaded as well. Here´s a demo vid:
Jeskola Buzz is a free modular software music studio environment centered around a modular plugin-based machine view and a multiple pattern sequencer tracker. It´s been around since 2000 and includes lots of plugins. To see/listen what is possible with it, here´s a full production session with it by Roman Buehler:
Last but not least there´s a community forum for Buzz.
Cyan/n is a free Max app for creating sample based compositions by Katsuhiro Chiba. Development has stopped in 2008 but this is still cool. This is what you´ll get: Slicer · Looper · Rhythm box with 4 tracks granular · Multi effect and Master effect etc are integrated and can be processed in real time without stopping performance. The user interface is laid out so that you can quickly access all parameters, and it also supports external MIDI controllers. Site is is japanese.