Formally the "Nexus 5 Real Volume Booster" the app has been renamed to comply with Google's policies

Is the speaker or headphone volume too low
on your otherwise fantastic Nexus 5™?
 

Nexus 5 Real Volume Booster 
is here to the rescue!

Boost your speaker and headphone volume without adding any distortion.

Specifically developped 
for the Nexus 5™.

The only app to offer distortion free audio boost for your Nexus 5™.
Nexus 5™ is a trademark of Google Inc.