Sure, Lucidchart is awesome.

But have you considered these open source alternatives?

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

Check by yourself: Excalidraw , D2 , tldraw , Draw.io , Mermaid Live Editor .

So is Excalidraw

Quadro branco para desenhar diagramas com aparência de feitos à mão
★ 130K Diagram Whiteboard License: MIT
Um quadro branco virtual de estilo desenhado à mão em código aberto. Colaborativo e criptografado ponta a ponta.

Read more about Excalidraw
So is D2

Turn text into diagrams
★ 25K Diagram License: MPL-2.0
A modern diagram scripting language that turns text to diagrams.

Read more about D2
So is tldraw

Digital whiteboard with infinite canvas
★ 49.9K Diagram License: MIT
Tldraw is a library for creating infinite canvas experiences in React. It's the software behind the digital whiteboard tldraw.com.

Read more about tldraw
So is Draw.io

JavaScript, client-side editor for general diagramming
★ 62.7K Diagram License: Apache-2.0
Browser-based diagramming components and applications.

Read more about Draw.io
So is Mermaid Live Editor

Edite, pré-visualize e compartilhe gráficos/diagramas mermaid
★ 6.8K Diagram License: MIT
Edite, visualize e compartilhe gráficos/diagramas mermaid.

Read more about Mermaid Live Editor