What is GTD app for iOS with subproject tree?

Question

iOS

Please advise subject.
Since there is a whole bunch of similar software on the usual request "gtd" in the appstore, I will immediately clarify the criteria:
1. more or less strict adherence to the GTD process, and not just a decorated tasklist;
2. built-in calendar or integration with native iOS;
3. most important! - nested projects.
Those. I need a project tree.
Synchronization with some web service would be a nice bonus. Within 1k rubles, the price is not important.
At the moment, Toodledo fits my criteria, but it has a catchy client design; I bought it, tried to use it, but realized that it would not give me pleasure, which means that I would not use it. Here, I'm looking for analogues.
Thanks in advance for your advice. The software that I eventually install will be marked as a solution.

Answer 1

todoist

Answer 2

Once used "Priorities". There is definitely a tree there, there was no calendar at that time. There is also a web version.

Answer 3

I also looked for software with similar functionality, but did not find it. Projects are best managed in OmniFocus, but there's no calendar. With a calendar, there are probably only Calendars and Fantastical, but these applications are more likely for the average user.