Problems with Rhino
Rhino development started at Netscape in 1997 for an ill-fated "Javagator" project and was released to Mozilla.org in 1998. It was then licensed to Sun and others. Honestly, 1998 might as well be the Jurassic Period, as Internet development goes -- 16 years later, Rhino has clearly shown its age. According to Jim Laskey of Oracle, the principal developer of Nashorn:
I'm sure this is all true, but as a jaded developer and development manager I find the last sentence highly amusing. After all, major rewrites are never fun. Starting from scratch is always fun.