Getting Things Done (GTD) web or cross-platform app

Question

I'm looking for a Getting Things Done type application with some scheduling capabilities.

Here are the features I need:

1. ability to automatically reschedule a task either from the last time it was done, or from when it is actually done, according to at least all of the following:

   • every N units (days, weeks, months, years)
   • every Day of Week (i.e. Sunday, Monday, Tuesday, etc.)
   • every DOM (1st, 6th, 18th, etc.)
   • any combination of 1, 2, and 3, for instance, "Every 6th and 18th of each month", "Every Sunday, Monday, Tuesday, Wednesday, and Thursday" etc.
   • Ability to specify a combination with an offset, for instance, "The 3rd Tuesday of each month", or "The next Monday after the 18th of each month".

2. ability to specify when a task is due and the estimated amount of time to complete

3. cross-platform (with data synchronized between platforms). Android and Mac OS X are the two most important platforms, although if the solution works in any web browser (including mobile) that would meet this requirement.
4. ability to export data at any time in a standard format like CSV (data not siloed)
5. ability to generate current tasks (today's tasks, this week, etc.) in a format useful for sharing with others
6. should not be too informal when talking about its price
7. should enumerate its features on its website (or here)

Optionally:

8. Allow times to be defined for certain contexts, and then generate a tentative schedule for a given time frame including repeating tasks under the assumption that each will be done when initially scheduled.

A couple that I have tried:

DGT GTD

1. Doesn't provide the ability to do combinations of date or offsets, but otherwise is the most complete I have found so far.
2. Does this very well
3. Doesn't seem to support many platforms. I have the Android app.
4. Data seems to be siloed
5. Doesn't seem to have a way to share

Nirvana

1. Reschedule support is atrocious. Provides only every N units.
2. Appears to provide this support.
3. Seems to be very cross-platform.
4. Data is exportable.
5. I have not found any way to share.

For pay is okay, as long as it's not more than a couple dollars a month. If I have to sign up for a longer period of time like a year to get a price break that's okay too.

Answer 1

I've decided on using Doit.im. It doesn't fully meet all of my requirements, but it's about the closest I have been able to find.

Here's how it's features match up:

1. It can't do combinations or offsets, but for now I work around this by creating multiple identical tasks. For example, if I need to do a task on the 6th and 18th of each month, I create two otherwise identical tasks, one for the 6th of every month, and one for the 18th.

2. You can specify a scheduled time and a deadline. Assuming that there is no time for other things in between (not always a valid assumption) the amount of time estimated is calculable from the other two.

3. Works on all major platforms, although I have noticed that I sometimes have to explicitly sync things done on my phone if coverage switches between 3G and Wifi around the time I am doing stuff. Maybe I am just not patient enough for the retry delay or something.

4. There is an API (although it seems a bit rough around the edges) and a separate task exporter someone wrote in javascript.

5. I haven't played with this too much, but I don't think the support is there yet. I can always screen capture today's schedule or this month's and send it to somebody, but that's a bit clunky.

6. Formal enough. Price is $2/month or $20/year. When you sign up you get the Pro version free for a month to try out. For my current needs it will probably be adequate, and in a year I will have time to re-evaluate.

7. Features are discussed under "Help".

8. I can see a monthly calendar view of scheduled tasks.

A couple of notes: You can do a hierarchy of tasks, but you are limited to four levels, which are called Goals, Projects, Tasks, and Sub-Tasks. Certain things can't be done at certain levels. For instance, you can't associate extra text with a sub-task or schedule it. I have seen some questions in the Doit.im forums where the ability to do more levels of hierarchy were requested, and the response from the developer was pretty strange, as if they couldn't even understand why that would be useful.

It doesn't seem possible to reschedule at task that is finished late. I have certain tasks which should be done every 2-3 days, but if I am a day late on a two day tasks, the task cannot be done the next day, it has to be done in two days. It is a bit of a pain to fix these cases.