Is there such a task scheduler?

Question

Task Management

I am looking for a task scheduler with the following requirements:

• Cross-platform or web interface - it is important that you can manage all this business both from a PC and from a phone
  
• Infinite subtasks - so that for each task you can add a subtask to it too and to it too...
  
• Ability to run a backend server on your own
  
• The ability to attach comments, photos, videos, documents, etc. to the task.
  

Answer 1

redmine?

Answer 2

Taiga.io and  alternatives .

Answer 3

Bitrix24 has everything you need.