This is a NES music arrangement of Clouds, the Windows 95 easter egg song.
I'm not going to describe the easter egg in detail, but the song was written for Microsoft by Brian Orr. He describes the song as well as the easter egg on his site here.
The original MIDI file ("clouds.mid" can be found here.
Oh yeah, this is my first post, let me know if I'm doing anything wrong. OK?