Thanks for your question on Tracker for ArcGIS. Tracker is currently available for Enterprise 10.7. Online will be available in late June.
The iOS and Android mobile apps are pending release to the relevant stores and should be available within the week.
You can access our EA site using this URL; https://earlyadopter.esri.com/key/LocationTracking. You can also view the doc for Tracker which is available here: https://doc.arcgis.com/en/tracker/help/configure-location-tracking.htm
If you have other questions or run into problems, let us know.
Tracker for ArcGIS team