Programs and literature on business planning (startups, small businesses)

Question

Startups

Please share your knowledge.
In particular, I want some software or service that would allow me to make and calculate a business plan.
I imagine something like a Gantt chart where tasks / purchases / expenses and their cost are scheduled, and when you move tasks back and forth in time (and change the estimate), the cost and payback are automatically recalculated.

Answer 1

better than Excel has not come up with anything yet)

Answer 2

The very first request to Google gave a rating of such services
online-business-plan-services-review.toptenreviews.com/ I
guess that you could do it yourself and want reviews from those who used it ... but, alas ...