I know Dropbox sync is available for the iphone, but I use Android. What follows is long praise of Thinking Rock from somebody that dreams of switching back.
Having been a TR fan for years now, I'm actually not using it. For the better part of a year I've been using other products. Mainly to comply with a corporate no wifi policy, so I badly need sync over mobile network.
I sadly miss Thinking Rock. TR is true GTD and I am a big believer in that. The weekly review with TR is perfect, and fun. Many great moments in my life were with TR doing a weekly review. It sifts your stuff though David Allen’s workflow and decision making process.
All the other apps are gtd workarounds. I should blog the comparison, because I have tried and bought just about everything else Android based. For example Remember the Milk does not have contexts. Toodledo has a workflow that is 95% gtd, but you would not believe the difference that 5% makes. While Tracks is pretty gtd, the UI falls quite is nothing like thinking rock. Having the Inbox that asks the gtd questions when you process is just brilliant.
The one thing that was amazing with these other apps, is syncing on the go. Ubiquitous capture, and make use of idle time is so easy with sync being driven entirely by the phone over mobile network.
Appreciate the great work by the thinking rock team.