Nginx has the Push Stream Module, which is similar but not quite as versatile. I don't think you could implement the "incremental counter" API described in the Pushpin article, for example. Whether or not this matters to you comes down to how much control you need.
I'm not aware of such functionality in HAProxy but would love to hear about it (I'm an HAProxy fan :)).
While "incremental counter" is a cool idea, I fail to see how it really improves anything. You're just moving the same problem from one layer to another. Node.js does all Pushpin does and you can write "simple chat server in 30 lines of code" as well, without the need to set up another piece of software.
This look like band-aid for developers still stuck with Python, PHP, whatever... technology from 2000's. I see I've got a down-vote from fanboys already, but that's just the way HN works: it's hard to have a constructive coversation, but it's easy to hate.
P.S. @jkarneges, this reply was not directed at you, but whoever down-voted my simple question. I mean, how can you down-vote a question? Let's not question anything and spread love, a la Facebook "like-button-only" style. :(
I've upvoted your original post to see if that helps.
The article does play up the compatibility with legacy frameworks. However, the proxy approach itself was designed independently of this, and the versatility turned out to be a bonus. Some background:
http://blog.fanout.io/2013/02/10/http-grip-proxy-hold-techni...
Basically, I'm positing that as a system gets larger, then moving the problem to an outer layer is good design, even if all of your backend code is event-driven. You can use Pushpin and Node together with a straight face. :)
I'm not aware of such functionality in HAProxy but would love to hear about it (I'm an HAProxy fan :)).