When I do runs on my treadmill it's very easy to maintain pace, because I can set it on the treadmill.  

However, when I run outdoors it's much harder for me to maintain consistent pace.  Are there any Apps that can help track my speed/pace? Could I perhaps use any cadence device and app to tell me via my headphone to slow down or speed up to maintain a certain cadence that I want?  

As I move out of my indoor treadmill winter running to outdoor running I want to make sure I'm staying a good cadence throughout my run.  Thanks for any advice guys.

I use my Garmin watch to track it. It shows it real time (slight delay, maybe 2-3 second delay as you speed up or slow down) then saves it in the app.

I have a Garmin forerunner that tracks my pace and distance using GPS.    It can display current speed, average pace, time, mileage, cadence, and a few other parameters that I forget.   I usually have it scroll through my heart rate, current pace, average pace for current mile, time, and distance.   It combines a few of these on the screen and I think it scrolls through 3 different screens.

For a free app, you can use Strava on your phone

Find a spotify playlist curated for your desired cadence. Tons of options.

cadence =/= pace