Question: Do you know of a text editor that offers a high level of customization and supports integrations with diagramming tools like draw.io?

First, AiEditor is an open-source next-gen rich text editor built with Web Components. It can be integrated with tools like draw.io and excalidraw for virtual whiteboarding and diagramming. AiEditor has a lot of features, including AI-powered spell and grammar check, text expansion and compression, real-time collaboration with commenting, and customizable configuration options for custom layouts and UI tweaks.

Another choice is CKEditor, a JavaScript-based text editor that offers a modern, feature-rich and highly customizable way to create a wide variety of content. It supports real-time collaboration, AI-assisted writing and content import/export to PDF and Word files. CKEditor also can be easily integrated with popular frameworks like Angular, React and Vue.js, so it can be used in a variety of situations.

For diagramming, Lucidchart is a cloud-based intelligent diagramming app that enables real-time collaboration and helps turn complex ideas into interactive diagrams. It includes AI-powered tools to automatically generate diagrams and integrates with Google Workspace, Microsoft, Atlassian and Slack. That means it's a good option for a lot of teams, including IT and engineering, project management and education.