bbPress.org

We aren’t including Snoopy, only WP_Http (which is only around 24k of code if you discount the comments)

The cron job is triggered by pageviews and then only if there are jobs to run.

So on a visit to the site, the cron job list is checked (just an option in the meta table) then if there is something there to do, bbPress sends an HTTP request to itself, which the user doesn’t need to wait for.