ZionEdit can run multiple independent edit windows that can be placed and sized however you want. This makes side by side comparisons easy. Locations and sizes can be specified by start up switches.
In order To maintain a robust development system ZionEdit employs WxWidgets Inter Process Communication to ensure data (like history and style changes) is coordinated between windows. IPC also ensures that you don’t accidentally open a file as writeable twice.
ZionEdit is based on the out-of-this world Scintilla edit component. So all the standard editor features are available. Some are still on the to-do list, I do confess.