If you came from Windows background and you wanted to try creating applications that will be used for Android and iOS but you don't have Macintosh machine, then you can try to use Mono from Xamarin.
They have been working closely with Microsoft in the past to provide open source platform which is compatible with Microsoft's .NET specifications and now, they want to improve it much further by adding support to iOS and Android SDKs.
For iOS, you might want to try Mono Touch and Mono for Android is for Android. Both projects are updated frequently and they are keeping up with the latest version of SDK available by both vendors (iOS 5 and Android 4 Ice Cream Sandwich).
Since it's .NET based, it's well integrated with Microsoft Visual Studio and since it's also available for Mac, you can also use XCode as your IDE and use .NET classes in your
MonoTouch apps. You can also easily bind existing C and Objective-C libraries.