Hotaru CMS is an open source, plugin-powered content management system. Think of it as “WordPress without blogging”. If WordPress didn’t do blogging by itself, you’d need plugins to do it for you. And if you had to make plugins, you wouldn’t be limited to just blogging. You could make plugins for any kind of site, whether a blog, a social network, an online shop, etc. That’s Hotaru CMS, a framework for making websites customized to your needs.
Hotaru CMS Features:
Here is an ever-changing explanation of features available in Hotaru CMS, some built-in, others provided by plugins.
User registration includes anti-spam measures such as ReCaptcha, email validation, a “blocked” list, a plugin for StopForumSpam.com and options for a starting role: pending approval, under moderation or regular member. Furthermore, you can have moderators notified of new registrations by email.
With the RPX plugin, users can register and log in with third party providers such as Twitter, Facebook, Google and Yahoo. This is a fantastic way to increase the number of people that register for your site.

Hotaru perfect CMS for Social bookmarking site.