This is probably the most useless device I have made. It displays random tetriminoes on a 4x2 LED matrix. It has two modes: one where it automatically displays a new tetrimino every few seconds, and one where it requires a button press to display a new tetrimino. It has a PIC18F26K20 for its processor.

EDIT: Some updates and pictures and other fun stuff
I added a blinking effect whenever the tetrimino is changed, and I also added an LED for showing if the timer is activated or not.
Here's a video: https://www.youtube.com/watch?v=Z0nJXMi7fSQ
Here's a better circuit diagram: http://i.imgur.com/zztkk1E.png
And here's the code: http://pastebin.com/aS8vF9ZW

That would require 8 more LEDs, and too much programming

Wha, that's looking sweet ^.^

Wait, Tetris on paper? O.o That must take a long while to play lol and I assume that some of the challenge is removed? It sounds like an interesting idea to try, though.

When I was bored in the study hall, I programmed calculator games. But I had to hold the calc in a way that looks like I am doing school work and calculating so that it doesn't look suspicious (although my school work was finished by then, the teacher might not have know and might have thought I'm just slacking off instead of doing it)

Also nice video and update