I stumbled upon Agenda Hero by chance - and what a lucky find it was! Out for a stroll and you see a poster for a cool concert? Open Agenda Hero on your phone, snap a picture - and the date is in your calendar. See an announcement on Insta? Snap a screenshot and Agenda Hero creates the perfect calendar entry. This is the tool I've been waiting for! (and I only miss this feature: how about somehow including the source image in the calendar entry?)