Really nice to see Deepstream being on the front page of HN!
I'm currently using Deepstream in production for one of our clients in-house applications, so unfortunately I can't share a link. I'd like to give a few words on why I chose Deepstream.

TL;DR
Deepstream is really good!

When I first found Deepstream and scimmed through the docs, I instantly noticed how thoroughly planned and well-thought it was. The features Deepstream offers ended up making us able to drop REST HTTP completely. Normally when you build a back-end, you have all your application logic in one place (authentication, CRUD API, sending emails, etc) but the way RPC's and Providers in Deepstream are implemented, you want and can easily write your back-end as microservices. For example, you build a client that recieves RPC calls for hashing passwords, and if that client starts getting under heavy load, you can instantly spin up another instance of that client and connect to the Deepstream server, register for the RPC and Deepstream server will then distribute the RPC requests evenly among the two instances. Normally when you scale, you scale the entire back-end. Deepstream allow you to scale parts of your back-end really easily (e.g the part that sends emails, the part that hashes passwords or the part that crops & scales images). This allows for some really efficient fine-tuning of your back-end.

Another awesome feature is Providers. Providers can do a lot of things, for example transform a standard third-party HTTP REST API (e.g Facebook) into an integrated record list in Deepstream that is synchronized in real-time. Another example is writing an efficient real-time provider that integrates with literally anything - filesystem, databases, logs, hardware utilization, nginx requests, third-party API:s, w/e. The capabilities of Providers are endless.

Deepstream is insanely fast - I've worked with Meteor & other real-time solutions before and Deepstream simply outperforms them by a long shot. This is mainly thanks to the Cache Connectors that are available, for example the Redis Cache Connector. Writing Storage- or Cache Connectors is really simple and straight-forward and seamlessly integrates with any kind of storage you want. Heck you can even write a Storage Connector that stores its data in Firebase if you want to be really crazy (and idiotic). Or maybe in a GitHub repository? These are just stupid examples to illustrate how extendable Deepstream really is.

I've just scratched the surface of Deepstream, so I really suggest that you go explore it yourself!

I see a lot of questions regarding how Deepstream differs from Socket.io, SocketCluster, Meteor, etc. I'll go through each respectively a bit:

Socket.io is nothing more than a WebSocket server. Both Deepstream and Socket.io uses Engine.io (can be configured in Deepstream) behind the scenes, but comparing the two would is not really optimal as Deepstream is Socket.io plus a ton of additional features and performance improvements. You can technically re-build Deepstream by using Socket.io if you want.

Meteor is quite similar, but it has additional features (like being a full-stack framework) and their implementation of real-time sync is really bad. Meteor is by default locked-down to MongoDB and it's a pain to write support for any other database as they've also locked you down to the fibers coroutines and you need a client-side implementation of it as well for caching purposes. The number of connected clients the two supports is massively in Deepstream's favor, and Meteor doesn't even come close to being as distributable as Deepstream is. Believe it or not, but I used to work with Meteor until I found Deepstream.

SocketCluster and Deepstream are very similar, and unfortunately I haven't tried SocketCluster apart from reading the docs but to me, Deepstream is more developer friendly and straightforward and looks to have a better implementation. Since SocketCluster is on the front-page of HN as well, just looking at the live example they have on their website shows that it's not able to keep up. The WebSocket connection is dropping a lot.

For those of you who use front-end frameworks like Angular/Aurelia/React/Vue/etc you'll find it super simple to integrate Deepstream's client directly into the bindings of the framework. For example (Aurelia): `<input type="text" value.stream="pets.husky.favoriteToy">` would setup three-way bi-directional databinding to `pets/husky` on the property `favoriteToy`. (I'm currently in the process of doing exactly this for Aurelia)