It’s called “Site-wide Content”, and what it does is basically add a copy of the post or comment that was just published in a custom database table. This allows us to efficiently query a single table, instead of making a complex query for dozens, maybe hundreds of tables.

Currently there’s no widget support built-in, just API (similar to the WP Query class). However Atom themes like Mystique have built-in support for this plugin, right now only in the “Posts” and “Recent Comments” widgets:

It’s not yet ready, but I’ll be updating this article when it is