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

    手書きのような図を描くためのホワイトボード

    ★ 88.3k diagram whiteboard License: MIT

    オープンソースの手書き風バーチャルホワイトボード。 コラボレーション機能と端末間暗号化に対応。

    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