Get lots of free samples/patchs for iOS apps or as Wav files from Electronicsounds (Donations possible).
DefleMask is a free (Donations possible) cross-platform chiptune music tracker.
It is available for Windows, Mac OS X, Linux, iOS and Android.
If you’re on iOS and you want a MS-20 emulation as AUv3 for free then look no further.
Because of the Corona virus, Moog has made the Model D freely available for now for iOS.