Good MIDI editor?

[Spare-Flair]

I've just bought a new keyboard that can take midi inputs, but a lot of my midi files are randomly collected over the past 10-15 years and some of them are incompatible or arranged with the wrong instruments incorrectly.

Is there a good free midi program out there that can let me join instrument parts and change the order of tracks, etc.

I've been using a clumsy go around of using GuitarPro's midi import system to do it.