Given the proliferation of several mobile device platforms, namely iOS and Android, applications should be available on all these platforms. Rather than rewrite code to make the applications available on each platform, several toolkits have been created to support cross-platform development. These cross-platform development toolkits are designed for regular applications and games. Popular toolkits for regular applications include the open-source PhoneGap project, AppMobi, and Appcelerator. Popular toolkits for mobile games include Unity and Corona.
I do not have enough information to report on similarities and differences for Unity and Corona toolkits. Unity appears to be the most popular from what I’ve heard.