Documentation software recommendation

Hello folks,

I have made a software and am looking for platforms where I can make a nice flowchart, diagram or similar stuff to show the entire flow of my project.

I wanna ask all the people in big techs & MNCs – What software/platform do you all use?

For now, I know of these: Excalidraw, Draw.io, Luicdchart etc
(P.S: I am looking for a free alternative)