MIDI Software

Wikipedia has a list of editors available.

Split Poly Plugin
Plugin to split chords into separate channels.

Editing best practices:

• Google is your friend, you can download nearly every song in midi.
• Reorganize the channels coud be really useful in some tracks.
• Clear out the doublenotes and chords.

Could be useful this tool, writen to make midis more playable in monophonic synthetizers: https://github.com/tg44/MidiSplitter (split the chords to separated chennels)