The Windows version can read Macintosh Inspiration file formats. It is a more limited outliner in some ways, better in others. See Matt Neuberg's Tidbits review of Inspiration 4.0 and also Importing a GrandView file into Inspiration. A portion of it is an outliner built by some of the people who did MORE and its predecessors. Frontier 6 will also be able to read MORE2Text output into its enhanced outliner.
Some people claim to like it.
I think Word has evolved into an abomination that's given both outlining a style sheets a bad rep. If Microsoft ever did move to XML as a standard file format that others could write too, Word would actually become vulnerable to competition. I think they know that, and I do not expect Word to actually ever use a public file format. The current version of WordPerfect for Window is said by one user to have a substantially better outliner functions than Word. They took my complete outlining command set and integrated it into the program - no more macros.