It's Conway's Game of Life, but it runs on Google Spreadsheets! It's a bit slow, but it works.

1. Create a new spreadsheet in Google Spreadsheets.
2. Go to Tools -> Scripts -> Script Editor
3. Paste game-of-life.js into the window and hit save.
4. Reload the spreadsheet!

You should at this point have a new menu "Game of Life." If you choose, "Random Board," you'll get a random start position. Choose "Gosper Gun" to get a known interesting start state. Then choose "Next Generation" to compute the next generation of the simulation.