I have three closed source apps on my phone:
Amazon Appstore - Solely for BubbleUPNP.
BubbleUPNP - I have not found a better UPNP app for streaming music to my audiophile Blue Ray player.
My credit union app - Self a explanatory, and doesn't require Google Play Services so I'm hopeful they'll offer it one day outside of the Play Store in light of the Aurora Store problems.
Nine Folders - An app for accessing all of my work emails and calendar, which sadly runs outlook. I'm looking to eventually ditch this app (which no longer is updated) and move to DavMail server.