Drop7 is my current favorite game.
I used to get on the leaderboard with it every day.
It's best on the iPad, because of the bigger screen. I started writing a clone of it in Ruby.
Unfortunately, I soon discovered Chain Factor, the original Flash version which Drop7 started life as. For days after I discovered Chain Factor, I didn't do any work on my Ruby clone. Or anything else, really.
I can't say I was surprised. I got on the leaderboard immediately, and at one point, two of the top ten scores for basic mode daily were both mine.
I've open-sourced my Ruby clone, and any further dev I do on that will happen in public on GitHub.
Here's my command-line clone.
As you can see the command-line version lacks the special effects of the iOS version. No shock there, I hope. I've also created a very basic Web UI:
As much fun as I've had with this thing, I'm going to recommend that you just buy Drop7. However, if you want to play with this, the code is on GitHub.