iMacros is basically a web browser based program for web scripting, editing and recording web automation tests. It's available as a freeware version and a commercial version. In a nutshell, the commercial version of iMacros has more features, better web scripting language support, various testing modules, bug-fixes and performance enhancements. On the other hand, the freeware version only has basic features and capabilities and the scripting language isn't quite as advanced. So if you want to learn WYSIWYG, iMacros should be great.
If you're into automation, have you ever tried to complete jobs like writing HTML, Java or PHP without spending hours trying to figure out HTML's code? With imacros, you can easily get an HTML form filling component to work right in your web browsers! This way you can test all kinds of HTML forms right from your computer. This feature makes it incredibly convenient to write forms and check the validity of them in real time! This is another reason why imacros are so popular - you can check your forms' validity anytime, anywhere, with imacros.