Procmail hasn't updated in over ten years. Maybe it's done.

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.