Go

Go's strengths are networking and services, and most of these tutorials play to them. Start with Eli Bendersky's REST Servers in Go (7 parts), which builds the same API with the standard library, then with routers and frameworks such as Gin, so you can compare the options. Let's build a URL shortener in Go with Gin and Redis (4 parts) and Building Go Web Applications and Microservices Using Gin are good follow-ups. REST API masterclass with Go, PostgreSQL and Docker is a long video course.

For something less like a web app, Jeiwan's Building Blockchain in Go (7 parts) builds a simple blockchain with proof of work, persistence, transactions, addresses and networking. Jesse Li's Building a BitTorrent client from the ground up in Go downloads real files and teaches binary protocols and concurrency with goroutines. Liz Rice's talk Building a container from scratch in Go live-codes a container using Linux namespaces and chroot in a few dozen lines.

Chat apps are covered three ways: Building a TCP Chat in Go (video), Building a Chat Application in Go with ReactJS (6 parts, WebSockets), and Create a Real Time Chat App with Golang, Angular 2, and WebSocket, now available through the Wayback Machine. Build Web Application with GoLang is astaxie's free book on web development in Go, and the Go WebAssembly Tutorial compiles a calculator to run in the browser.