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 ,  D2 , LibreOffice  LibreOffice .

  1. So is Excalidraw Excalidraw

    Lavagna per disegnare schemi come fatti a mano

    ★ 98.2K 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

    ★ 54K Diagram License: Apache-2.0

    Browser-based diagramming components and applications.

    preview

  3. So is D2

    Turn text into diagrams

    ★ 20.4K Diagram License: MPL-2.0

    A modern diagram scripting language that turns text to diagrams.

    preview

  4. So is LibreOffice LibreOffice

    Office suite

    ★ 3K Office suite License: MPL-2.0

    LibreOffice is an integrated office suite based on copyleft licenses and compatible with most document formats and standards. Libreoffice is backed by The Document Foundation, which represents a large independent community of enterprises, developers and other volunteers moved by the common goal of bringing to the market the best software for personal productivity. LibreOffice is open source, and free to download, use and distribute.