Okay, let me preface this with "I have not tried any of these types of calandars yet". Keep this in mind as I mention my must have's and desires of any calandar application since some may fit all of these.
Currently I use Outlook 2007 at home (part of the Office suite I got) and Lotus Notes at work (blech, but I don't have a choice). What I am looking for from an application like this is not really just a calandar, but a full featured PIM. That said, the calandar portion is what I will focus on due to the jist of the post.
First and foremost, the application should work on/with a variety of handheld devices including Blackberries, iPhone, and Windows Mobile (I only use the last, but the other two are where the money is now, so if you are doing it, you might as well make it work for all). However, I do not want it to be a web only app, as I am not web connected 24/7 (data plans are way too much for personal use!), though a web synch option may be desirable for some.
Now for the application details.
1. It should be able to read Outlook, Lotus, Groupwise, Yahoo Mail, Live Mail, and GMail options at a minimum. I know these are all email apps, but they all have calandars associated with them. These calandars should be able to synchronize with the program.
2. Any unsupported features should not be discarded, but rather ignored, so as the data moves, the unused parts could still be accessed when brought back into the originating program. (This should be standard for ALL collaboration software that claims to work with any other system!)
3. It should support multiple calandars per person, and multiple people independently while associating the groupings if appropriate. For example, I have a home calandar and a work calandar that I can turn on or off separately. Joe has the same. If I want to turn on all his appointments and only my work appointments, I should be able to do so while knowing which appointment belongs to which person and which calandar for that person. I would suggest color coding the calandars, then grouping by user with a faded background color per user. Maybe there is something that does this already, but it is just one idea for an implimentation.
4. It should also support alarms. What good is a calandar that doesn't remind you of your appointments? I have seen some good implimentations of calandars that don't support alarms. Useless to me....
There are several more, but I can't think of them at the moment, and I don't have my compiled checklist here. I will look into it later and hopefully post back with more. Anyone have any suggestions so far?
Now, to be fair, it is time to look at VueMinder to see how close they come to these requirements....