Hotknot
Is a Media Tek feature that lets two devices transfer data (like photos or contacts) by touching their screens together. It's like NFC but cheaper and less common, and mostly found on older phones.
DEMO
#Mediatek

Visualizer
#Sony

Center status bar clock
#OnePlus

Dual microSD
#Saygus

Notification pinning
#ASUS

Cyanogenmod Privacy Guard

EDIT: Early version of app ops
don't mistake it with Android 6 permissions

#Cyanogenmod

Gesture search
#Google

Z Launcher
#Nokia

HTC Sense Home widget
Smart homescreen panels based on your location.
#HTC

WhisperPush
#CyanogenMOD

LG TV Remote app
App used both IR blaster and Gyro to control LG tv just like their magic remote
#LG

Ringtone ID
#LG

Magic focus
After opening the camera app and pressing Mode, choose the Magic Focus and line up your shot. You’ll need to hold the camera steady, as one press of the shutter button will actually take five photos. Once the images have been stitched together, head into the gallery and use the slider on the far right to chose which image to keep, or tap the “all in focus” button to focus on the entire scene.
#LG

O-Touch panel
You could use gestures on your back to:
Scroll
Open camera
Take photos
Record
Control music
#Oppo

One touch backup
#Sony

Washable phone with soap and water
#Kyocera

Sharp Pantone 5
Radiation Detection
#Sharp

Clari-Fi visualization
#Sharp