Version 6.1.2 is out and I hope you'll take the (brief) time to upgrade. This version includes several bug fixes and ensures that all videos, tabs and projects created by Java Tracker can be opened by Tracker Online.
To upgrade, click the green "Now available" button on the toolbar and choose Upgrade Now. If you don't see the green button choose Help|Check For Upgrades.
You can also download installers directly from the Tracker home page (http://physlets.org/tracker/) or ComPADRE (http://www.opensourcephysics.org/items/detail.cfm?ID=7365).
I am having a problem with the installation of version 6.1.2 on Windows 10. The application is not opening in any window. Has this issue been reported by anyone else?