It was already asked here
some time ago, and the accepted answer was Cakewalk by BandLab
, which is a free product, like a free beer. It is not extremely complex, but I would not say that it is "simple" either. It has a lot more functionality than MIDI recording.
Another software that I know is MidiEditor
, which is free software (open source). It is simpler than Cakewalk, but there should be probably something else more simpler.
If you were using Linux instead of Windows, I would say that arecordmidi
is the simplest, but I dont know anything equivalent for Windows.