Please take a look at the 1 star reviews. They are from users who are upset that their version of OmniGraffle, version 5, which was released over a decade ago in 2007, is not compatible with macOS High Sierra. They believe OmniGroup is greedy and unfair for expecting them to upgrade to the latest version, even at a discount, and are demanding they make it free. If you wonder why most companies are moving to subscriptions, these users are why. They believe if you buy an app once, you should never have to pay for an update or upgrade, regardless of the work required to make it fully compatible with an OS released a decade later, or the many features and improvements added. I really wish Apple would pull these reviews as they are useless to someone considering buying the app, but I digress.
I wonder about these people. Do they pay their auto mechanic once and expect him/her to work on their vehicle for free as long as they own it? How about their barber/stylist? One time payment and free cuts for life. Or is it only software developers who they believe should work for free?
OmniGraffle has been, and remains, the very best diagraming tool on Mac and iOS. The OmniGroup is a dedicated Mac team which utilizes extensively macOS features and continually deliver apps that are best in class in terms of UI design, functionality, and performance. If you need a diagraming app, then you should should strongly consider OmniGraffle. Download it and take advantage of the 14 day free trial. I think you’ll find it to be worth every penny.