Android Wear 2.0 has plenty of improvements and changes, but one that has plenty of people excited is having apps installed on, and running from, the watch itself instead of the connected phone. In the past Google had said that this wasn't optimal and would lead to a bad experience, but hardware improvements and Android just getting "better" have brought this change.
The three apps are Glide, Foursquare, and Lifesum. The Glide app will use the Communications API to let us do things like stream directly from the watch or initiate a conversation with someone without getting our phone involved.
Foursquare will use Android 7's new rich notifications so that you'll get more information — and the information you want — right on your watch instead of being directed back to your phone for it. Nougat's notifications were built on the original Android Wear card system and should make for a better experience anytime your watch needs to tell you something.
The Lifesum app for Android Wear 2.0 is designed to track meals and water intake directly from the wrist. Cutting out the phone component means you'll always have fresh data available and changes will be reflected instantly.
You can have a look at the latest developer preview builds of Android Wear as well as all the documentation at the Android Developer site.