What are some alternatives?
When comparing Adobe InDesign and OmniGraffle, you can also consider the following products
Sketch - Professional digital design for Mac.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Canva - Canva makes design simple for everyone. Create designs for Web or print: blog graphics, presentations, Facebook covers, flyers, posters, invitations and so much more.
draw.io - Online diagramming application
Adobe Illustrator - Adobe Illustrator is a vector graphics editor.