adx is a minimalistic but massively Web-enabled address book that runs completely in your Web browser. It's OS-independent and supports comprehensive details for each contact entry, including user identifiers and profiles for Skype, Twitter, Flickr, Delicious, Facebook, LinkedIn, studiVZ, instant messengers, etc. It supports the hCard and XFN microformats.
Tactor is a tool that tries to guess the best action for the current text selection. For example, text containing http://xyz.com is recognized as an URL link, and ~/Documents/MyPresentation.key as a presentation file. Both matchers and actions are fully customizable. It is loosely based on Plan9’s Plumber where any text can potentially be an action, although the actual technical implementation is very different. It provides functionality somewhat similar to that of Apple Data Detectors in a way that is fully extensible and transparent.
Google Calendar Chrome Extension adds a button to your browser toolbar that displays a preview of your calendar while you're navigating. (works on any page). If you're on certain sites where it detects the presence of events, the icon changes to a green "+". Clicking that icon lets you add the event to your Google Calendar, and shows you a Map (if there's a location it could detect.) Supported sites include Facebook, Evite, and any site that uses the hCalendar microformat or derivative microformats such as hResume.