In addition to powering full blown web apps, web technologies can also be used from within web views to create hybrid native/web apps.
I have a post on idevblogaday.com today on calling Objective-C from JavaScript, calling JavaScript from Objective-C, and logging to the Xcode console from JavaScript.
I made an app called RipDeck based on the deck of cards workout that is great for providing variety to your routine.
We have a weekly featured deck or you can create custom decks. Great for bodyweight exercises. Give it a try. https://itunes.apple.com/us/app/ripdeck/id409921624?mt=8
The featured decks are available on the site if you want some workout ideas for use with a regular deck of cards. http://ripdeckapp.com