I worked with Mary Robinette Kowal to set up the Achievements plugin for the Month of Letters BuddyPress site. Members earned badges for sending various kinds of mail, and cumulative points for the number of letters or packages they sent. These were reported via a Gravity Form tied to a custom post type, with a taxonomy that provided the checkboxes for the types of mail (parcel, Valentine, overseas).
Because Achievements was in between versions when the event started on February first — 2.x was deprecated, but 3.0 was not quite out yet — I wrote several custom tools and widgets for the site. The code for each badge also had to be done by hand, since they were tied to a custom post type.
When the site’s traffic overwhelmed its shared host a few days into the event, I did an emergency migration to WP Engine, where it’s been stable (and much faster) ever since.