A browser-based IDE based on pipelines, isolated execution steps and notebooks.
A chat service with threads, topics, custom emojis with the possibility to run your own server.
And not a single one of them ticks all the boxes.
A visual programming language for machine learning.
A set of patterns and techniques to work with Web Components. It won't solve inherent problems of design like not being able to de-register a custom element but definitely a good read if you plan to lean on Web Components for your web app or rich page.
A book on types of networks (WiFi, 3G/4G), transport protocols (UDP, TCP, TLS), application protocols (HTTP) and Web APIs (XHR, WebSocket, WebRTC).