friendiversary is the anniversary of when you became friends with someone, a feature supported by some silos like Facebook as part of their on this day support.
If you post when you meet someone (e.g. "Nice to meet you URL/@-name") then your publishing software could remind you a year later, prompting you to message them.
In the past some bloggers would post XFN "met" posts linking to people they meet.
Today there is no (new) publishing/format convention(s) for such "met" posts, so you may have to develop one for yourself, e.g. try looking at your own organic "met" posts to see if you can discern a pattern, and write software to remind you in the future.
None so far.