Tools Directory: Isso
Comments written in Markdown
Users can edit or delete own comments (within 15 minutes by default). Comments in moderation queue are not publicly visible before activation.
SQLite backend Because comments are not Big Data.
Disqus & WordPress Import
You can migrate your Disqus/WordPress comments without any hassle.
Configurable JS client Embed a single JS file, 40kb (12kb gzipped) and you are done. Supports Firefox, Safari, Chrome and IE10.