I cringe a little whenever I see someone try to solve an issue with planning and productivity that's already been covered years ago by awesome systems like GTD

I cringe a little whenever I see someone try to solve an issue with planning and productivity that's already been covered years ago by awesome systems like GTD - especially when they try to solve it with technology. I want a tool, not an infomercial-esque "solution." To be constructive -- in order to make this useful as a tool and retain the central value-adding idea, make sure you include tags and tag filters at the very least. That's all you need to make it both simple enough for casual users and versatile enough for power users. I can't tell you how many tools I would love to try but can't because they don't have tagging or replace it with something not versatile enough (like nested lists). Foremost among those is Google Tasks.