Bumblr is a new QML/Qt based Tumblr app for both Harmattan and Symbian platforms.
The app is still very much in progress but if you are looking for nice looking Tumblr app, this just might be it. Symbian version of Bumblr is available for download, while you need to wait a bit longer for Harmattan version.
You can follow the progress of the app from here: http://talk.maemo.org/showthread.php?t=86713
Download Symbian version from here: http://code.google.com/p/bumblr/
