Precisely four years ago, the first ever changeset with #MapComplete was made. Granted, it was a testing point - but it marked the birth of MapComplete:
openstreetmap.org/changeset/85…

Tomorrow, there is an OSM-meetup/birthday party for it: osmcal.org/event/2867/

OpenStreetMap-meetup + MapComplete birthday party

(English below) Een gezellig samenkomen voor iedereen die interesse heeft in OpenStreetMap - van totale beginner tot expert.

^{OpenStreetMap Calendar}