To get the list of activities/applications installed on Android:
final Intent mainIntent = new Intent(Intent.ACTION_MAIN, null);
mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);
final List pkgAppsList = context.getPackageManager().queryIntentActivities( mainIntent, 0);
Referred from: How to get a list of installed android applications and pick one to run
To check all running applications
ActivityManager actvityManager = (ActivityManager)
this.getSystemService( ACTIVITY_SERVICE );
List<RunningAppProcessInfo> procInfos = actvityManager.getRunningAppProcesses();
Referred From: http://www.dreamincode.net/forums/topic/138412-android-20-list-of-running-applications/
Note: Above described function will return correct result for below API 21, for 21 and above it's deprecated.
