Backwards compatability and Mac requirements

How backwards compatible is OmniGraffle and how much can I ignore upgrades?
Like if everyone else on a group project is on a newer version, will I have to constantly bug people for older versions?

Also, what are the minimum mac requirements?

Basically I don’t want to have to buy a mac just to use OmniGraffle, but if I do then I would like to not spend too much money.

I don’t think the file format has changed for a while. I have used since early 7 series and no file changes noted; almost all the upgrades are for functionality as far as I know. Kind of where new features are hitting a bit of a road block in terms of maintaining compatibility. Maybe when they go to version 8?

For requirements, you can check the App Store and