Paul at www.dynamicadventures.co.uk wanted a web-enabled calendar so that his team could coordinate their events. As they run all sorts of outside activities, and could be travelling anywhere in the UK or beyond, having an office-server calendar would not help.
They had managed well enough with the Yahoo calendar but it had a major limitation: they wanted to be able to see which staff were associated with with event, at a glance. This meant having colour-coded names showing up on the month and week views.
I spent several hours of research and was surprised to find what a large number of calendars were available, both open-source and shareware. Gratifyingly for me, most of them were in PHP, my stock in trade. But the second surprise was that none of them catered for this seemingly straightforward (nay, generic) requirement. This would mean I'd have to start with a near-miss app, and get out the spanners for some tinkering under the hood.
After many trials I finally settled on the opensource WebCalendar from k5n. This is very capable but not (quite) overwhelming in its plethora of configuration options. I used it based on MySql but it copes with other flavours of database too. Out of the box, it already allowed you to associate named participants with an event. The participants were known names from a table (not freetext) so I simply added an extra column configuring a colour for each person; and then amended the display code to show the names on the page under the event title.
All of which adds up to a hearty recommendation for this calendar, if you are looking for something similar. It didn't let me down.
Disclaimer: This calendar is not open to public view.