Neptune also experimented with a new HTML and Win32-based user interface originally intended for Windows Me,[5][6] called Activity Centers, for task-centered operations.

[7][8] Only one alpha build of Neptune, 5111, was released to testers under a non-disclosure agreement,[2] and later made its way to various beta collectors' sites and virtual museums in 2000.

In response, some Windows enthusiasts have spent years fixing Activity Centers in build 5111 close to what Microsoft intended.

[14][15] In early 2000, Microsoft merged the team working on Neptune with that developing Odyssey, the successor to Windows 2000 for business customers.

Neptune was intended to have a successor named Triton, which was to be a minor update with very few user interface changes; service packs were additionally planned for it.

Triton was devised back in 1998 alongside Neptune; the only details of it within Microsoft's internal planning documentation that year relates to a deadline for added hardware support by December 2001.