This program lets you play music and videos on a window that can be chromeless, controll-less and always-on-top, if you so desire. When this starts up, it has a bunch of buttons and UI, but you can use the following keys to control your experience:

W to toggle the window border, which lets you resize
P to toggle the player controls - to pause, play and change the volume
A to toggle always-on-top behavior, if you want the window to not be hidden by other windows
F to pick a file or playlist to play
B to toggle the buttons toolbar.

Download the source code.
Download the binary.

This program and its source code is licensed under the BSD 2-Clause license.

Last updated sometime in 2007.