Annotator is a jQuery plugin that allows you to store annotations of anything on your web pages. There is also a bookmarklet available that enables you to create annotations across the web.
The plugin itself is extensible with a number of plugins (packaged & third party) that allow you to do things like save annotations to a web store, tagging, authentication & authorisation and much more.
With WordPress managed hosting only WordPress sites are allowed on the server. That allows the server to be incredibly well optimized for the WordPress platform. Plus, you literally don’t have to do anything that relates to your server. If you are a beginner who is starting a blog, then you DO NOT need managed WordPress hosting. You should start with regular WordPress hosting which is a lot more affordable. You could either hire a system admin to manage your website, or you can use a managed WordPress hosting provider. Learn more about wordpress hosting for single sites at the link.
If you are using Wordpress, a plugin is available here.