Address Book Server allows you to share your contacts and calendar events with others connected to your network or over the Internet. Each participant synchronizes their contacts with the server hosted on your own system. Address Book Server supports the full Address Book and iCal schema. The server also provides a friendly Web interface and an iPhone client which let you access your contact details remotely.
DAViCal is a server implementation of the CalDAV protocol for storing calendaring resources (in iCalendar format) on a remote shared server. An increasing number of calendar clients support the maintenance of shared remote calendars through CalDAV including Mozilla Calendar (Sunbird/Lightning), Evolution, Mulberry, Chandler, and various other closed-source products such as Apple's iCal and iPhone. DAViCal supports basic delegation of read/write access among calendar users, multiple users or clients reading and writing the same calendar entries over time, and scheduling of meetings with free/busy time displayed.
Googsystray is a system tray app for Google Voice, GMail, Google Calendar, Google Reader, and Google Docs. It lets you keep track of the information provided by those services without having to keep a bunch of Web pages open or constantly checking them. It notifies you of new events, such as messages or alerts, and provides basic services quickly.
GCalert will access all your Google calendars and display alarms via libnotify for whenever you have alarms set for each event. These alarm widgets do not receive focus (and thus do not take keyboard input away from other applications), yet are clearly visible even on a cluttered desktop.
tngCalendar is a Web calendar addon to the TNG software for online genealogy. It adds a convenient view of your family history, overlaying anniversaries of births, deaths, and marriages on top of an easy-to-understand calendar. It can be dropped in-place over a commercial TNG installation, or installed in a parallel directory.
Tasktop Pro adds productivity features and connectors to Eclipse Mylyn. Tasktop Pro extends task focus to your time tracking, Web browsing, and desktop documents. It includes connectors to Firefox, Google GMail and Calendar, and Outlook/Exchange email and calendars. You can easily install additional connectors to Atlassian JIRA, Crucible, Rally, and CollabNet. Tasktop Pro is available with connectors to IBM ClearQuest and Danube ScrumWorks.