Internet Explorer's web technology, often using the then-new Mars framework. A key focus of the Neptune project was to experiment with user experiences that did not require manually saving previous work; some of this effort is visible in the only available build, which enables hibernation by default and requires the user to take extra steps to fully shut down the device.

In early 2000, Microsoft merged the team working on Neptune with that developing Odyssey, the successor to Windows 2000 for business