Solaris jumped from 2.6 to 7 (the "2." is now implicit). Of course, Windows NT jumped from 4.0 to 2000. ;)

Java went from 1.4 to 5. Although not completely; it took until 9 for the actual directory names etc to change.

But it didn't, really. NT 4.0 was followed by NT 5.0 (branded Windows 2000) and then by 5.1 (Windows XP) and then by 6.0 (Windows 7).

Vista was 6.0. Windows 7 was 6.1 and 8 was 6.2 (8.1 was 6.3). They finally bumped up the version to 10 with Windows 10.