I'm going to show you how to make a Twitter powered Death Ray. No, it's just a gumball machine. But, the principles are the same; so, if you want to make a Death Ray and think that Twitter is the best way to power it (it probably isn't), have at it.
The technology behind Tweet-a-Tweat is Arduino + ThingSpeak. The Gumball Machine is from Beaver Vending and has an Arduino inside listening to the TweetControl App from ThingSpeak. TweetControl listens to the Twitter stream for keywords that trigger HTTP requests in real-time. The heavy lifting happens in the cloud so that the embedded Arduino only has to focus on moving servos and being ready for web requests.
Get your gumball at http://www.tweetatweat.com/