diagrams.net is a cross-platform diagramming application available as a free online app, a desktop app and in a number of integrations.
We maintain the draw.io integrations for Confluence and Jira, specifically. draw.io on Confluence is a good way to move the single source of diagramming truth inside Confluence, since the creation and edit workflow is tightly integrated.
draw.io is capable of both importing from Visio and exporting out to .vsdx.
Fore more general info on draw.io for Confluence or Jira, please refer to our draw.io webpage.
And some great blogposts! Blog - draw.io