SSI is designed to be a simple alternative to authentication systems such as OpenID. The plugin is designed to work on most WordPress installations, and it allows your Wordpress installion to be both a provider(allows you to sign in to ssi sites) and a consumer(allows others to sign in to yours). It also allows you to manage your login information. In addition to that, those that post comments on your site after signing in also have their avatars displayed and the comment form is autofilled for them. SSI is designed using RESTTA , meaning that is a protocol open to any application that implements it.