Much like Gist, Tungle was acquired by RIM quite some time ago and since then, have maintained their separate services but now that time has come that they too, will be shutting down. They've now sent out emails to folks letting them know the services will be shut down entirely as of December 3rd, 2012 so that they may continue on their work at RIM and BlackBerry 10:

Tungle began in 2006 to make finding times to meet with colleagues, clients and contacts as quick and easy as possible. In April of 2011, we were acquired by Research in Motion (RIM) with the goal of bringing the Tungle vision to millions of BlackBerry customers. After our acquisition we quickly went to work and built the BlackBerry Playbook Calendar app. Now, our team is creating the native Calendar app for the next generation platform, BlackBerry 10, and together with other key RIM employees, we are driving innovation in Messaging (email), Contacts, Notes and Memos apps.

All of our new responsibilities within RIM are very exciting; however, it hasn’t left much time for innovation on the core Tungle product over the past year, as we’re sure you have noticed. To make the most of our new focus, we have sadly decided it is time to shut down the standalone Tungle service.

As of Monday, December 3rd, 2012 we will shut down the standalone Tungle service. You will continue to be able to use your Tungle.me page until then to schedule meetings and share calendars. We know our dedicated members rely on Tungle every day to manage their calendars and we don’t want to leave you out to dry, so we suggest you check out Doodle to replace Tungle in December.

We appreciate all the support you have given us over the years and hope our efforts on BlackBerry 10 will bring the same dedication and excitement.

While it's sad to see them go down entirely, it's nice knowing they'll be including their great services in BlackBerry 10. Thanks, Robtanz!

Read the full announcement on the Tungle site