To get a list of running processes on Android 1.6 - Android 6.0 you can use this library I wrote: https://github.com/jaredrummler/AndroidProcesses The library reads /proc to get process info.
Google has significantly restricted access to /proc in Android Nougat. To get a list of running processes on Android Nougat you will need to use UsageStatsManager or have root access.
Click the edit history for previous alternative solutions.