When you run it, a small window pops up above your taskbar, and displays the message "Drop files to play". That's about it. You can hit a little down arrow and minimize it to tray, or you can leave it open. While it's in the tray, you can control it by the tray menu (pause, next, previous, etc), and you can even make it "Track change popup", which will bring the main dialog up for a second when a new track plays, then hide it again.
The program has Shuffle, and even a playlist. Clicking a clipboard in the main dialog will show a playlist of whatever songs you've dragged onto M3, almost like a "Now Playing". You can even search the list!
M3 is surprising, in that it looks nice (even though I am quite partial to black), and it works nicely. It has everything you could want, except maybe volume controls. I need to comment on one thing though, and that's the transitions between tray and dialog. It's very smooth, and doesn't look clunky.
Overall, it's a wonderful little music player, amazing for its size. It's also very light, only consuming 7mb of RAM when playing, around 4 when idle. It's also portable, meaning you can take it anywhere. What's also nice is that you can pass a music file as an argument to it, meaning you can make it the default handler for song files like MP3s.
The only, literally only, thing I can find fault with when it comes to M3 is file support. It is a tad limited, as it is only able to play MP3s, WMAs, and WAVs. It would be nice if it could play AAC, OGG, or even FLAC, but it is just a tiny 100kb music player. Considering how much smaller it is than the other music players out there, I'd say three formats is definitely enough to make it a great find.
M3 may be a tad limited, but it is very good at what it does. It's fairly new, v1.0, released Feb 2009, so drop a line to the developer, and let him know what you think of it. And if you happened to want to tell him that you heard about his software at FreewareWire, well, that'd be mighty fine as well.