I think you meant 2000s because in the 90s Solaris was nothing special. All the interesting stuff (zones, SMF, dtrace, ZFS) was introduced in Solaris 10, which was released in 2005.
As I recall, solarix had Doors by 2001, but I can't remember what it was.
Solarix probably deserves mention if Tru64 nee OSF/1 did. Ah, the Unix Wars: Sunview vs. Motif, buggy vs. ugly.
Ken Thompson (interviewed by Brian Kernighan, 2019, starts after 7m38s): https://www.youtube.com/watch?v=EY6q5dv_B-o#t=7m38s
Rob Pike (Unix History presentation, 2018, starts after 3m40s): https://www.youtube.com/watch?v=_2NI6t2r_Hs#t=3m40s
I strongly recommend anyone with even a vague interest in UNIX (well, obviously that would be everyone reading this HN thread) to watch these!
This is now on my Amazon wish list (How many of you have private lists for 'things to remember and check out later?' Mine's called 'Random Followup Stuff')
It's Kernighan's view of Pascal after writing "Software Tools in Pascal". It's not (as widely perceived) a hit piece on Pascal. It's Kernighan saying "I wrote the original 'Software Tools' in Ratfor. Rewriting it in Pascal should have been much easier than it was. Why?"