The server-side part of pg:diagnose is a go program I open sourced at https://github.com/heroku/pgdiagnose . It'd be easy enough to run locally for your own stuff, probably.

From a cursory glance it seems to be a pretty presentation layer on top of http://www.postgresql.org/docs/9.3/static/pgstatstatements.h...

If you use Rails, there's https://github.com/ankane/pghero . Other frameworks / languages have equivalent projects, but I haven't used them. But in the end, the data comes from querying special views in database, so it's easy to roll your own if you so desire.