HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Hyvor Talk - The Best Commenting Platform For Your Website
Crucial Human - Crucial Human makes software focusing on human productivity, collaboration, and learning.
Commento - A fast, bloat-free comments system to foster discussion on your website