Presque vu: is a French term which means "almost seen". It is the feeling of very nearly, but not quite, remembering something.
Here are three operating system projects that attempt to recreate or provide the look-and-feel and user-experience of other operating systems. They are driven by fervent nostalgia, but could they, will they, ever be "even better than the real thing?
1. ReactOS - Aims to provide an implementation of a Windows® compatible OS
2. Haiku - Aims at the re-creation of the Be Operating System.
Haiku OS homepage"
3. CoLinux - port of the Linux kernel that allows it to run alongside another operating system on a computer. Run Linux on Windows® 2000/XP.
Cooperative Linux Homepage