Tracker & Tracker Online are continuing to work together more and more seamlessly, and both use Library Browser to access the same collections. Now, in version 6.2.0, Library Browser is improved in three ways:
--Collections can include many types of resources: Tracker projects, videos, images and image stacks, zipped image stacks, EJS simulations, Data text, HTML pages, PDF documents, general URLs (eg YouTube videos) and links to other collections. --Tracker Online can be opened with a specified collection displayed in the Library Browser. For example, here's the Tracker Sampler collection: https://physlets.org/tracker/trackerJS/?j2sargs=https://physlets.org/tracker/library/cabrillo_collection.xml --Library Browser can run on its own, without Tracker. In this case it launches Tracker projects in 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).