There are a lot of standalone JavaScript runtime built on various engines like V8 but in order for them to qualify as an alternative to node they must be actively developed and designed to be used as back-end for web. These really narrows down the list; with that in mind here are the alternatives to node js.

Deno

Deno is a JavaScript/TypeScript runtime built with V8 JavaScript engine, (the same as Node js). It was created by Ryan Dahl, the original creator of Node.js, in 2018. Are you thinking what I'm thinking?

Deno Claims to provide a more secure and efficient runtime environment for JavaScript and TypeScript development, Deno includes built-in support for features such as TypeScript, WebAssembly, WebSocket, more modern and secure approach to handling modules, file system access, network operations and implements fetch API* (a pain point for many Node developers which is fixable with the Node-Fetch API only starting with the Node version 17.5).

Deno does not use a package manager such as npm. Instead, it uses a more modern approach where modules can be imported directly from a URL. Documentation, tutorials, and examples can be found at Deno website

Deno is relatively new so it's not as widely adopted as Node.js but it is getting there. As for speed; they are almost the same with node having slight advantage generally performance is a big argument among developers. Your Node js project are not easily migrated to deno.

Bun

Bun is a JavaScript runtime that stands out for its speed and built-in bundling & transpiling features. Developed using the Zig programming language, Bun constructs its runtime on the lightning-fast JavaScriptCore engine, used in Apple’s Safari web browser. It was released in 2022 by former Stripe developer Jared Sumner.

Other runtimes rely on outside tools for bundling your JavaScript projects and for transpiling code from another language. Bun handles all of these features. It also implements the Node.js algorithm for resolving modules. This means that Bun can make use of NPM packages. Bun’s bundler can find and install packages from the vast NPM repository and manage their dependencies, it also comes with first-class support for the TypeScript and JSX languages.

Bun claims to offer some advantages over Node.js in simplicity of tooling and speed. Documentation, tutorials, and examples can be found at Bun Website

Have you tried any of these alternatives? please share your experience.