This article is from the comp.sys.acorn FAQ, by Paul Vigay with numerous contributions by others.
Before Acorn decided to abandon Workstations and focus on Digital TV, work was at an advanced stage on an updated version of the operating system (codenamed Ursula) to live in their new machine (Phoebe). Developers had access the RISC OS 3.8 (as Ursula declared itself to be) for evaluation and beta testing purposes. Versions of RISC OS 3.8 were primarily available for ARM710 machines, although some StrongARM compatible versions are known to exist.
For those who don't know, Phoebe is a character from the hit US sit-com Friends, and Ursula is the name of Phoebe's twin sister.