Convert astdb back to berkeley db 1.86
cd astvarlibdir && astdb2bdb path/to/astdb.sqlite3
Up until version version 11, Asterisk used an old version of the Berkeley DB 1.86 (bdb) to store its internal persistent database. In version 11 it switched to using a SQLIte 3 database. This program is used to convert the newly-formatted SQLite 3 astdb back to bdb.
You may need it in case of reverting an upgrade or other similar scenarios.
There is a single (and required) parameter: the path the the sqlite file. The output file will be a file called astdb in the current working directory.
In case you want to revert an upgrade to Asterisk 11, you can do the following (while Asterisk is not running):
cd /var/lib/asterisk && astdb2bdb astdb.sqlite3 && rm astdb.sqlite3
This will convert the newly-formatted astdb back to the old format, and delete it (to avoid obsolete data copies).
Berkeley DB 1.86 is obsolete. It is incompatible with newer versions (4.x and newer) that you may see around. Chances are you don't have the tools to use it independently of Asterisk.