[sgaur]

Thanks for mentioning Visio, it is now available on the browser as well for basic, business, flowcharts, network, and cross-functional flowcharts. $5/per user/per month (annual plan) https://products.office.com/en-us/visio/visio-online-plan-1

Disclosure: I work for the Visio team, so if you have any feedback pls lmk.

[xpil]

What drives me absolute bananas is the way they changed licensing for Visio. You could get the database reverse-engineering feature (Pro version) for a fixed, one-off price up to some point. Now it's all subscriptions. Blah.

(great software though, I have to admit)

As for the main topic, my favourite diagramming tool is GraphViz, mostly because it is easy to script / automate, does a great job auto-placing things, handles large diagrams quite nicely and works on any OS.