The only other PIM I know of is Pocket Informant. I have tried it and didn't find a compelling reason to use that instead of the standard PIM features of my BlackBerry. It runs independently/separately from the built-in calendar/address book clients. Since they're not linked you have to sync them periodically. When you enter a calendar appointment into Pocket Informant it does not automatically go into the BlackBerry calendar as well. I didn't like that. I also wanted a weekly grid view, which PI provides, but its formatted all wrong. I wanted a vertical layout like a paper date book, but PI's week-at-a-glance view is horizontal. Not user-changeable either.
Still, you may want to take a look.
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