Crowd is a Web-based single sign-on (SSO) tool that simplifies application provisioning and identity management. It has connectors for popular open source projects like Apache (via Perl) and Subversion. Pre-built connectors for other popular commercial products like Jive Forums, JIRA, and Confluence are also available.
Google Apps Improved Login (GAIL) provides Google Apps administrators with two oft-requested features: the ability to customize the login page and the ability to log in as their users. GAIL is designed to run on Google's App Engine so that administrators do not need to have their own Web server. GAIL works by making use of the SAML Single Sign-On (SSO) Service for Google Apps. Premier and Education Editions of Google Apps are supported. Standard Edition is not.
LemonLDAP::NG is a modular Web SSO based on Apache::Session modules. It simplifies the building of a protected area with a few changes in the application. It manages both authentication and authorization and provides headers for accounting, so you can have full AAA protection for your Web space. LemonLDAP::NG is a complete rewrite of LemonLDAP. All components needed to use it and to administer it are included in the tarball. However, all modules developed for LemonLDAP may not work with LemonLDAP::NG.