This extension was interesting years ago when 9.0 to 9.3 releases were still maintained. So, this won't be updated since the feature it delivers it now on every maintained PostgreSQL releases.
mods_since_analyze is a PostgreSQL extension that exposes the estimation of number of changed tuples on a table since last analyze through the function pg_stat_get_mod_since_analyze(oid).
The pg_stat_get_mod_since_analyze() function is originally written by Mark Kirkwood for PostgreSQL 9.4 release. It's been commited in the PostgreSQL git repository (see commit c87ff71f374652936a6089215a30998492b14d52). Many thanks to him, and his reviewer (Albe Laurenz), and his commiter (Magnus Hagander).
This extension allows anyone to get this information on older releases (from 9.0 to 9.3).