I believe he's referring to the SharpTools for Android app which provides a set of Tasker plugins including some nice event driven plugins that can trigger actions in Tasker based on events in your (SmartThings) hub.
It's on our list to add support for Hubitat to the SharpTools Tasker plugins, but we've found that most Hubitat users have been getting by with the Hubitat Maker API and using one of the push options.
Note that Join is just one option for pushing messages down to your device. Personally, I use Pushbullet to send messages from Hubitat down to my phones/tablets (via the SharpTools.io Rule Engine), but I understand that Pushover is a popular alternative on the community and even has a native driver built-into the platform.
Pushover has a one-time $5 charge per 'platform' that you use it on. (eg. $5 for Android and $5 for iOS if you use both). To use it, just go to the Devices screen in Hubitat, create a Virtual Device, choose Pushover, fill in the name and ID, and once the device is created be sure to fill in your Pushover API Key in the device preferences.
If you want to use Pushbullet, you can either use the driver by rayzurbock or connect the SharpTools.io Rule Engine to send pushes. 
Pushbullet's free tier has a 500 message limit per month.
