Sure, Visio is awesome.

But have you considered these open source alternatives?

They are free, self-hostable and community-driven.

Check by yourself: Excalidraw  Excalidraw , diagrams.net  Draw.io .

  1. So is Excalidraw Excalidraw

    Lavagna per disegnare schemi come fatti a mano

    ★ 88.3k diagram whiteboard License: MIT

    Una lavagna virtuale open source in stile disegnato a mano. Collaborativa e crittografata end-to-end.

    preview

  2. So is diagrams.net Draw.io

    JavaScript, client-side editor for general diagramming

    ★ 51.8k diagram License: Apache-2.0

    Browser-based diagramming components and applications.

    preview