The simplest CRM / fancy TODO list. Which?

Question

CRM

Today I thought about optimizing the workflow with clients.
And I see a piece of a similar plan.
From the system administrator.
System - there is a list of projects. When creating a new item, a long url is generated that can be accessed by any person with client rights.
Each project is a to-do list with the ability to comment on each item, add different types of files and the ability to close the task with a different status.
From the client side.
Minimal interface.
Login without registration.
You can add and remove (but not those created by the administrator) tasks.
Comment, add files, close tasks with different statuses.
The system should focus on the interaction of only two specific people and a spartan interface (no margins and paddings at 50px, everything should be as compact as possible, no extra buttons, no animations and shadows).
Don't care about safety.
It will be a bonus if the client has the opportunity to subscribe to updates by mail.
UPD.
Login without registration is very important. I do small projects on fl.ru Clients are always new, there are no permanent ones.

Answer 1

asana

Answer 2

Shared Google Spreadsheet.

Answer 3

codecanyon.net/item/clientengage-project-platform-...

Answer 4

Hesk or otrs

Answer 5

dynalist.io is awesome . At least what I was looking for.
the developer stole a lot from Workflowy and improved it.