Please see the blog post and watch the videos! Although the videos show PyScripter, the underlying editor control is SynEdit.
Note: Development of SynEdit has moved back to pyscripter/SynEdit: SynEdit is a syntax highlighting edit control, not based on the Windows common controls. (github.com) for the reasons explained here. The multi-caret developments are in the multicaret branch, which will be merged to master after a period of testing. It is quite solid, but if you would like to try and help iron out bugs, that would be much appreciated.