Let me add some more information about this.
There are two features that we just released: API Express and Offline Sync.
API Express allows you to expose a relational database via REST API
Offline Sync allows you to build apps with offline capabilities.
As API Express exposes a database via REST REST APIs, you can use the APIs in jQuery Mobile app and in AngularJS app (Bootstrap/Ionic). You can call the API from any other app (language of your choice).
The API Express extension does work with AngularJS apps right now. It generates services that use the Offline Sync library and connect to the exposed database via API Express. A better name for the extension might have been Offline Sync extension.
API Express exposed services will work with jQuery Mobile apps. You simply create REST APIs and then add then in the App Builder (Create New Service REST). This works just like any other API.
You can even add the Offline Sync library to your jQuery Mobile app but that will require a little bit of work. We are looking into adding the Offline Sync support to jQuery Mobile apps as well.
Hope this make sense.