miniforge is the community (conda-forge) driven minimalistic conda installer. Subsequent package installations come thus from conda-forge channel.
miniconda is the Anaconda (company) driven minimalistic conda installer. Subsequent package installations come from the anaconda channels (default or otherwise).
miniforge started a few months ago because miniconda doens’t support aarch64, very quickly the ‘PyPy’ people jumped on board, and in the mean time there are also miniforge versions for all Linux architectures, as well as MacOS.
Soon there will also be a windows variant (hopefully also for both CPython and PyPy)
I guess that an ARMv7 (32Bit ARM) variant is also on the horizon (Raspbian)