Google Assistant has added a "Your Actions" shortcut at the bottom of the Explore tab that, when pressed, shows a handful of actions you have linked, with the option to view a full list. This is the first centralized location for this information; previously, it was hard to tell which services you'd linked to Assistant and which you hadn't.
There are two sections to the Your Actions menu: linked and bookmarked actions. Linked actions are all the various services you've connected to your Assistant, and you're able to pin actions to the bookmarked section whether or not you've linked them to your Assistant, so it could be helpful if you're shopping around (so to speak) for new actions to add.
Tapping a service in the list will bring you to a page where you can rate, share, or bookmark it, while tapping the little speech bubble icon on the right side will perform the specific (seemingly random) action the card lists—for example, playing a certain song or artist in a music app.