EDIT: Commenting disabled for now, haven't had time to keep it up to date.
I wanted a simple light weight blogging engine, so I got Ghost. Ghost is so single purpose, that it has no commenting system.
Not wanting to use Facebooks comments, nor Disqus, I found no good alternative and decided to make my own.
Introducing Some Comments
Some Comments aim to be a generic commenting system that can be hosted separately from any page. It works with sites, pages and comments. Also single purpose, so it has no authentication of it's own (partly to not have to deal with spam-bots) but offers connections to login services like Facebook, Google, and will support OpenId endpoints etc.
The idea is to keep it small and good for it's purpose and nothing else. I plan to add administration pages for having multiple commenting sites in one installation, letting the user review and delete comments and connecting several authentication services to the same user account.
Right now (2015-05-16) it won't even notify the commenter of other's comments, but it's good enough to let you leave a comment.
Usage in Ghost
You are free to try out my installation if you'd like, with no guarantees.
Register your domain on Some Comments sites and get your site ID.
Add the following in your themes post.hbs (replace 1 with your site ID):
<div class=\"comments\" id=\"comments\"></div>
<script src=\"http://fredrik.liljegren.org:1337/node_modules/markdown/lib/markdown.js\"></script>
<script src=\"http://fredrik.liljegren.org:1337/node_modules/q/q.js\"></script>
<script src=\"http://fredrik.liljegren.org:1337/client.js\"></script>
<script>
SomeComments('http://fredrik.liljegren.org:1337/').displayByPage(1, 'post-{{id}}', 'comments')
</script>
…and a css-link in default.hbs:
<link href=\"http://fredrik.liljegren.org:1337/comments.css\" rel=\"stylesheet\" />
Then you should be good to go! Let me know how it works.
License
Some Comments is released under the GNU AGPL. That insures that the program continues to be free. You are free to run it as a hosted service, but if you add anything, it has to be made available to the users.