Checklist Manager? Modern Ecco Pro??

Anyone ever remember a program called Ecco Pro?? Man that was such a great checklist manager! When I worked for The Man, I called it my virtual brain, since I put everything that I ever needed to remember in it, in some kind of priority order, categorized and cross-referenced. People were amazed at the information I had at my fingertips.

But alas it has been "abandonware" for over ten years now, and (surprisingly) nothing has come out to replace it.

So I thought I would post my quest up here where someone else may have found something close to what Ecco once was.

I have several 1000+ item checklists for my clients that I would rather not maintain in MS Project, and was on the lookout for a Checklist Manager program that could do simple checklists w/categories?? Something like Ecco would be ideal. Something Ecco like as a SaaS or running under Linux would be even better :) And yes, I know I could still install EccoPro, but I want to get something that my customers could also use.