How to create an automatically generated task plan?

Question

Project management

Good afternoon, there seems to be a simple task,
1. There are, for example, three projects, three tasks each
2. We give each task an approximate time estimate
Next, three questions:
Question 1. What program / service to find so that it automatically builds a work schedule of the form:
- the first task of the project one
- the first task of the project two
- the first task of the project three
- the second task of the project one
- the second task of the project two
, etc.
That is, automatically, sequentially lined up tasks from different projects in the work schedule.
Question 2. So that this list of tasks is grouped by structure into days, taking into account their duration. For example 8 hours.
For example, the schedule for the first day:
- the first task of the project one (5 hours)
- the first task of the project two (3 hours), that's it, one day is over.
The next day (continues):
- the first task of the project three (4 hours)
- the second task of the project one (2 hours)
- the second task of the project two (2 hours), that's it, the second day is over.
etc.
Question 3. So that when adding a new (for example, fourth) project, tasks from it can be easily included on the same conditions in an already generated schedule.
It turns out a global question - so that you can conveniently and quickly draw up a task plan for the coming weeks, taking into account, for example, 8 hours of the day, and several projects with different tasks.
I would be very grateful if you could suggest a solution!
Or please suggest your option for more convenient time planning?
To plan the parallel execution of several projects, and understand how much time they will take

Answer 1

www.ganttproject.biz
MS Project

Answer 2

Trello.com + add-ons.
For autotasks:
- echofortrello.com (easier)
- butlerfortrello.com (more complicated, but wider functionality)
For time analytics
- toggl.com ( upd . corrected url)
- plusfortrello.com
But automation of the form "tasks no more than 8 hours a day "do not get: you still have to schedule tasks "for today" with pens, and rightly so.