Question

Since the system should know about the available Activities as they are declared in the appropriate AndroidManifest.xml files which are evaluated during installation:
Is there a way to query these Activities?

Answer 1

Sure, have a look at PackageManager.getInstalledPackages method. Here is the example of printing registered activities names:

List<PackageInfo> pInfos = getPackageManager().getInstalledPackages(PackageManager.GET_ACTIVITIES);
for (PackageInfo pInfo : pInfos) {
  ActivityInfo[] aInfos = pInfo.activities;
  if (aInfos != null) {
    for (ActivityInfo activityInfo : aInfos) {
      Log.i("ACT", activityInfo.name);
      // do whatever else you like... 
    }
  }
}