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

    Доска для рисования диаграмм от руки

    ★ 91.2K diagram whiteboard License: MIT

    Виртуальная доска с рукописным стилем с открытым исходным кодом. Совместная работа и сквозное шифрование.

    preview

  2. So is diagrams.net Draw.io

    JavaScript, client-side editor for general diagramming

    ★ 52.2K diagram License: Apache-2.0

    Browser-based diagramming components and applications.

    preview