I project managed integrating a piece of software into six simultaneous other software projects using Lotus Agenda and continued to run/use Agenda for over a decade on various DOS emulators. It was an amazing product.

The magical assignment of items to categories was totally key for being able to do so much with it. I could type in:

Talk to Greg about next Monday's QA results for integrating Peter Pan into Zebra and Leopard.

That item would go into my "Greg agenda," my "QA agenda," the "Peter Pan" project agenda, the "Zebra" project agenda, the "Leopard agenda," and next Monday's calendar. Then at the various one-on-one meetings, project meetings, etc., the item was simply present in the meeting's agenda.

As far as I could tell by using it, Ecco's was Agenda with a Windows interface but without the automagic assigments. The need to use a combination of mouse + drop downs + explicit category assignments detracted a lot, in my opinion. Agenda the DOS app had been hyper-optimized for rapid data entry. Ecco could structure the information the way Agenda did, but they didn't get the easy-of-entry anywhere near the level of Agenda.

If you're bringing back Agenda, I will be eternally grateful! (Though as an OS X user, I'm hoping you'll have an easy Mac install :-)