What are the advantages of an SDI interface? Except in that one respect, the features of UR are cutting edge. But Kinook chose to buck the trend toward tabbed interfaces. Of course it is easy enough to open another file simply by opening a copy of UR, but MDI comes into its own when applied to infoitems, not to files.
These days the outline-based pims that provide for a tabbed interface for infoitems are: TexNotes and TexNotes Pro
http://www.gemx.com), InfoRecall (
http://www.phantech.com), WhizFolders Organizer Pro, and HyperClip (
http://www.risksoftworks.com). So it might be significant that the three that are arguably the most technically advanced, UR, Idea!, and MyInfo stick with a single document interface when applied to items (MyInfo3 allows opening multiple files in tabs). So maybe there's good reason for sticking to SDI that I am unaware of.
Stephen Diamond