FreeBSD is also still very popular. The decline in popularity of FreeBSD would be more so to do with the rise in popularity and maturity of Linux and packaged Linux distributions.
Chandler (http://chandlerproject.org/) had a rather fantastic amount of money spent on it as an open-source project to no avail.
The BSDs are always dying. They do seem to be less influential than they were ten or fifteen years ago.
Enlightenment was popular before Gnome and KDE got better but it relied too much on one programmer and stopped updating.
Amaya was supposed to be the web's standard browser. It's still being produced, but last I checked it was a decade behind anything else in features.
I don't know how big the developer communities for any of them got.
"Work on Amaya started at W3C in 1996 to showcase Web technologies in a fully-featured Web client. The main motivation for developing Amaya was to provide a framework that can integrate as many W3C technologies as possible. It is used to demonstrate these technologies in action while taking advantage of their combination in a single, consistent environment." - http://www.w3.org/Amaya/
I don't think it was ever intended to compete with Mosaic or Netscape or Nexus or whatever was popular at the time.
Amaya is a reference implementation.