Managing entire IT development using diagrams

I have made a video https://youtu.be/jvw2uRQ64xE which describes how we manage IT development of our startup OrgPad using OrgPad. We are working on this tool for last three years and we are using it for everything ever since the beginning. I would love to hear your feedback.

Do you use diagrams for your development? Do you like sketching stuff on whiteboard? How do you plan new features or improvements to the code? How do you study some unknown technology?