Microsoft has announced the release of Visio Online so you can open and edit diagrams from just about any device. Although it will cost you an extra US$5 per month (assuming an annual commitment), that's pretty decent value. It allows your to share Visio diagrams which can be viewed for free using the iOS or online viewers.
Slowly but surely, all of Microsoft's core products are making the shift to the cloud. The past, even viewing files often required a license but that is changing as the company continues to embrace the cloud and deliver applications that don't solely rely on a computer running Windows. Anyone with an Office 365 subscription can view files.
The announcement of Visio Online notes that the cloud app offers templates for different types of diagrams, just like its Windows 10 sibling. If you've been using Visio Services for SharePoint Online, Visio Online will replace that service.
If you're an iOS user, there's a Visio Viewer available through the App Store.
There are two different plans to choose from, imaginatively named Visio Online Plan 1 and 2 although the local website doesn't seem to have up-to-date pricing just.