Mergely is a simple text differentiation web app that lets you compare and edit two pieces of text in your web browser.
When you get started, you'll be able to either paste two pieces of text into the boxes, or type up something new on the fly. If you paste in two, Mergely will highlight all the lines with differences so you can edit or change them if need be. It's an easy, quick way to compare files and edits online, with no need for a username or password. You can save the files and get a direct link to send to others for further comparison, or never save it and the contents are immediately removed.