Ryan Leavengood of Spectrum IEEE has written a detailed piece about the history of open source BeOS rewrite, Haiku. The article traces the project back to 2001, when the rights to BeOS were sold to Palm Inc. Developer Michael Phipps worried that the architectural advantages of BeOS, like native multi-threading and a utilitarian, vector based UI, would be forgotten if Palm lost interest in the platform, so he decided to rewrite it from the ground up. This marked the beginning of OpenBeOS, which would eventually be renamed to "Haiku" in 2004.
After 11 years of work from a small group of industrious volunteers, Haiku could move from alpha to beta this year, and if thing go well, a version one release could be out by this time next year. If you have an interest in an OS that has been sustained purely by the merit of its technical advantages, be sure to give Leavengood’s article a thorough inspection.