Google Fit is a pretty great free app which tracks your activity on your phone and gives a good amount of feedback, including a very cheery 'ping!' when you complete your steps for the day.
Now it has a new update and a companion app called Fit Challenge. This works with Android Wear and allows you to pick from a number of activities such as press ups. From there, the display will show you the proper way to perform the exercise with onscreen animations and then gives you a countdown for how many to do. During the workout you'll get helpful messages and you'll be able to create a program to follow for a set number of days.
All of this info is synced back to the mobile and desktop apps to give you a better idea of how your exercising is going, added into the way Fit passively tracks your walking and running activity. It sounds like a good way to get people to mix up their exercise routine, and you can get alerts to let you know when its time for a workout. Some Android Wear watches aren't set up to track the explicit data for all of these exercises but even a timer and a push from the app should be enough to get people moving.
The new app is releasing on Google Play now.