Doit.im

I think it is the best GTD app out there. I use it for all my task management. I particularly like and rely on the scheduled and recurrent tasks feature: it helps me pay bills and subscriptions on time.

[Edited by adrianfi, February 16]

Best GTD app for me.

Sync once per day is a archaic and ridiculous restriction for the free version. Calling it free is a lie, it's basically a demo of the paid version.

It has similar features to omnifocus, but works on windows and online

I have tried almost every single GTD soft out there. From macs things, through action complete, thinking rock, gtk gtd and many more. This one provides tbe best balance between usability, features and development. And of course price - you can not beat FREE. Dev team is extremely patient and they are very determinated to make this software the best.

[Edited by lebaux, November 03]
My previous excitement is over. App is now paid (but 20 bucks/year is a fair price!) if you want full sync options. Dev team is not responding very well in forums for requests - like the topic about export. After two years they have just closed it http://support.doit.im/entries/308767-export-or-print-view. Twitter is the same, they are responding but only PR and marketing bullcrap. Blog is filled with semi-useless tutorials, no info about the development of anything. I feel that they are group of stubborn chinese guys who are just doing it their way no matter what. Don't get me wrong, they made a great GTD/TODO app, but I am not so happy with it as before, because they do not hold onto promisses. This is however just my opinion. My recommendation here would be DGT GTD http://www.dgtale.ch/index.php?option=com_content&view=article&id=52&Itemid=61.