I tried this in my office roughly 6 months ago. No server required means one shared file contains all your shared calendar info. This caused two problems, first the program itself tended to hang when remote users were accessing the file, and when the person whose computer was being accessed crashed for some other reason, it brought the house down. We had only three people sharing one calendar, but it was not acceptable. Gave up and went back to Now with a dedicated server.
Consultant is a file-based application and has no server to facilitate sharing.
Sure, you can swap the data files around, but this is a sub-standard solution. It's a question of whether or not you can find one that fits your needs, not which one fits your needs best. I think that we're going to have to wait for something web-based because the market does not look like it's going to provide for us, especially if you want to run the server software on a Mac. Qualcomm killed Eudora Planner development. Once again, the answer may be Consultant.