What are the use cases of Node.js vs Twisted?

Twisted is more mature -- it's been around for a long, long time, and has so many bells and whistles as to make your head spin (implementations of the fanciest protocols, integration of the reactor with a large variety of other event loops, and so forth).

Node.js is said to be faster (I have not measured it myself) and might perhaps be simpler to use (if you need none of the extra bells and whistles) exactly because those extras aren't there (kind of like Tornado in the Python world -- again, I have never measured relative performance).

So, I'd absolutely use Twisted if I needed any of its extra features or wanted to feel on a more solid ground by using a more mature package. If these considerations don't apply, but top performance is a key goal of the project, then I'd write a simple benchmark (but still representative of at least one or two key performance-need situations for my actual project) in Twisted, Node.js, and Tornado, and do a lot of careful measurement before I decide which way to go overall. "Extra features" (third party extensions and standard library) for Python vs server-side Javascript are also much more abundant, and that might be a key factor if any such extras are needed for the project.

Finally, if none of these issues matter to a specific application scenario, have the development team vote on relative simplicity of the three candidates (Twisted, Node.js, Tornado) in terms of simplicity and familiarity -- any of them will probably be just fine, might as well pick whatever most of the team is most comfortable with!

As of 2012, Node.js has proved to be a fast, scalable, mature, and widely used platform. Ryan Dahl, creator of Node.js quotes:

These days, Node is being used by a large number of startups and established companies around the world, from Voxer and Uber to Walmart and Microsoft. It’s safe to say that billions of requests are passing through Node every day. As more and more people come to the project, the available third-party modules and extensions grow and increase in quality. Although I was once reserved about recommending it for mission-critical applications, I now heartily recommend Node for even the most demanding server systems.

More formally, the advantages of Node can be classified as:

• Great community: It can be said that no other platform gained such community appeal in such a short period of time, it has hundreds of contributors and thousands of watchers in GitHub, and is being used by giants like Yahoo! (Manhattan project), e-bay, LinkedIn, Microsoft, and Voxer.

• NPM: Although having a relatively small core, Node has lots of packages available to extends its functionality to anything you may consider! Its all automated and being developed and extended actively, think of PyPI (pip).

• Scalability and Speed: Node's architecture and single threaded nature allows high scalability and speed. Specially after 0.8 release, its speed got really faster (benchmarks), which can be confirmed by a lot of large businesses using Node. The V8 core of it is also constantly getting better thanks to the current browser war.

• JavaScript: The core language of Node (JS) fits better for such server side usages, specially lambda functions, dynamic objects, and easy JSON serialization are JS highlights which really fits well in cases that speed and scalability counts. (Python has all of them but these are really better and more powerful in JS).

• Deployment: Because of its wide usage, a lot of really good sites provide tools for easy and powerful Node deployment, including: Heroku, Joyent, Cloud9 and a lot more.

Therefore, Node seem more powerful and with a lighter future, so if there isn't any constraint to use it (like existing code, servers, team capability), it is recommended for any new collaborative network project aiming high speed and scalability.