I've kept my calendar online since around 2003, forward events publicly available throughout. Initially it was file-based with a two appointment records per day* in a text file per month, a few years later moving to a MySQL database, where it still resides. Currently at diary.alisonw.uk the domain has changed occasionally depending on which ones I happen to own at the time (!) and though the Internet Archive says it existed in 2005 their earliest copy - looking very similar to the current edition - appears to be from 2007**.
In the past it's been useful for family, friends, and lovers to check where I am (I used to travel a lot) and for me when booking appointments / finding out what I'm supposed to be doing.
* day, evening