I have just been very surprised discovering new functionalities of my small MP3-player. I'm actually so impressed by something that is probably old news (the particular model of the MP3-player is not even sold anymore), that I have to share it or I will explode.
The player I'm using is the Sansa Clip Zip, by Sandisk. I choose it because it's known to have pretty good audio quality, supports a bunch of different formats, has SD card slot, is small, but most of all, because it can run an open source firmware called RockBox (see http://www.rockbox.org/wiki/SansaClip#Sansa_Clip_Zip
). Of course I'm using that firmware, because it gives me a number of much needed features, such as gapless playback, FLAC format support, or the ability to skip whole directories. I have actually used that firmware for years on different Sansa players, as I broke or lost them and had to replace with the new models. It always worked great to me.
Today, when I connected my player to the USB port of my computer to re-charge it, I accidentally pressed the "play" button on it. And my computer started playing music. Surprised I investigated a bit more, and turns out that the player is seen by the computer not just as an USB disk, for copying the music files on it, but also as a keyboard, with three modes -- media keys, presentation and web browser. I can play music, change volume, switch slides, switch browser tabs, scroll the web pages, etc. with it.
Intrigued with that, I started to dig a bit more. I knew that the player has some plugins for it, such as a metronome or a snake game, but I never actually explored it in detail. Turns out that it has a lot more.
It runs DOOM. Yes, the 3D first person perspective shooter. You just need to upload a .wad file to it.
It has a GameBoy Color emulator. You just upload .gb files to it, and it will run them. The screen is only 96x96 on my model, so you can't really read the text in the RPG games, but it's good enough for the platformers and shooters. I see on Sandisk's website that there is now a version with 128x128 display, which should be much better, but sadly it's not yet supported by RockBox.
It has a number of other more or less useful apps. It has a video player. It has an e-book reader. A decoder for the resistor color codes. And so on. But those three features really impressed me the most.
Oh, and it has very good usability too. You can operate it without looking at the screen, it has audio feedback for everything, and you can even generate the speech files with titles of all your songs on your computer and upload it, and it will then tell you the titles of the songs! Especially recommended for vision-impaired people.