Don't most people who use Disqus just use the JavaScript to embed it?
At the pure tech level it's not equivalent. One required the ability to cut and paste and be done in a few moments, the other requires you to implement your own interface against the REST interface.
For a drop-in replacement, although not open source, I think moot.it looks pretty good: https://moot.it/
They're aiming at the embeddable market for comments and forums and have a pretty nice product.
Discourse is of course good on the open source side, but unless someone can point me at a JavaScript tool to allow embedding as simply as Disqus or Moot.it I think it's not the best match for this scenario.
As always... what's the full use-case? What are they trying to achieve? What are the priorities guiding the decision making process?
Discourse wins if the important criteria here is open source and the person asking the question is fine implementing the integration using the REST API.
Moot.it wins if you just want a drop-in replacement and that trumps the open source.
Writing your own wins if you want a project that will take far longer than you anticipate :)
Sam here from Discourse, I use Discourse to drive commenting on my blog and I love it, ever since I did it comment quality has gone way up. eg: http://samsaffron.com/archive/2013/11/22/demystifying-the-ru... , one could build a plugin that gives parity with disqus, its just a space we have not really decided to enter
Turns out that the extra click required and registration weeds out a lot of the problem comments.
I also find that giving people space, proper preview and excellent followup makes a world of difference (Discourse has reply by email, notifications and so on)
Originally I was considering adding a traditional, add anon comment box, but I am not really that motivated to do so.
Not yet very much integrated, but that shouldn't be a problem given the REST API of Discourse.