I would be happy to donate money for development.

There's a lot of tools out there for task / goal tracking. I'd suggest spending some time researching them before thinking about developing a new one. Beware of falling into the trap of chasing after the elusive perfect system rather than just getting in the habit of using something good enough.

I quite like remember the milk but my main problem is still the whole getting into the habit of using it consistently part. It's pretty flexible in terms of attaching extra information to items. It's not hierarchical but I suspect that's overrated anyway. It does support a very flexible tagging and 'smart lists' system which is better than a hierarchy in some ways.