I wonder what happened to bdb. I guess maybe authors lost interest/sold to Oracle and the license changed development just didn't keep up with the times. Bdb used to be the sqlite before sqlite existed and ended up used by various embedded applications or even graphical interfaces e.g. to index file thumbnails and such. I'm not sure but I think MacOS at one point used it this way.
I haven't even thought of Berkeley DB in years. Used to use it quite a bit but most notably perhaps with apache mod_auth_db to handle authentication and subscriber information on a fairly high traffic site (yes, this was long long ago ;) ).
