1. Groovy - a programming language, it rocks because it less verbose and more powerful than Java and I can fall back onto standard Java syntax when I don't care to figure out how to do something in the 'Groovy' way. (http://groovy.codehaus.org)
2. Gaelyk - a groovy framework that runs on Google App Engine. Google App Engine is great for launching apps. It's free until it gets traction. (http://gaelyk.appspot.com)
3. Objectify - The simplest convenient interface to the Google App Engine datastore. Takes a lot of the pain out of using Bigtable. (http://code.google.com/p/objectify-appengine)
These all pack a mean punch and let me work on my night/weekend projects quite productively after overcoming a small learning curve.
I built http://icusawme.com and http://chatroulettespy.com with all three.
I'm looking forward to diving deeper into Appcelerator Titanium Mobile in early 2011.