I just stumbled across this a day or two ago and think it's pretty neat!
UberNES Screen Saver (http://ubernes.com/nesscreensaver.html)
Here's a screenshot I just took of it running on my computer (native resolution is 1920x1200):
(https://lh6.googleusercontent.com/-jP3h5oxA2qA/T5BXTs3_5yI/AAAAAAAAD-A/_kH5x53QE_Y/s950/UberNES_Screensaver_Snapshot_120419_01.jpg)
You have to download roms and pre-recorded movie files (all are easy to get and take up very little space), but then when it's running you can use the arrow keys to select a game, make it go full screen and start playing at that point in the movie. When you take over the game the sound kicks in, otherwise it's silent. You can also control how many games it displays. At one point I had a 7x5 grid, but I could tell the computer was working to keep up, so I set it here, and also limited the screensaver to use 1 thread/cpu, another nice option.
I sure wish there was something like this for the Turbografx-16/ PC Engine library. That would be heaven. I'd never get anything done. :D