Project management system?

Question

Project management

Perhaps someone came across while working with this. We need a project management system that will allow you to create projects that have subtasks (checklist?), ideally so that the customer can fill and view them himself through access via a link, for example, or in some other way. Since there can be many small tasks on one project, and using Google tables is not very flexible and convenient... Thank you.
PS at the moment I'm looking towards BaseCamp, but I'm not sure that there will be what I need

Answer 1

Very simple and reliable Trello (much easier than Basecamp):
When you click on the card, the task modal pops up:

Answer 2

redmine?

Answer 3

Checklists seem to be in all popular task managers