Borescopes and videoscopes (aka. industrial endoscopes) are widely used in many applications to exam and inspect hard to see areas. 
High end videoscopes are usually articulating borescopes with small diameter (less than 6mm), where the small probe tip can be bended or rotated to see different directions.
Classified by viewer type:
Viewer (Eyepiece)
LCD Screen
USB to PC/Mac/Android
Wireless to Android/iPhone/iPad
Classified by insertion tube: Rigid, Semi-Rigid, Flexible
Insertion tube and probe diameter: 2.0mm, 2.4mm, 2.8mm, 3.0mm, 3.9mm, 4.0mm, 4.5mm, 5.0mm, 5.5mm, 6mm, 8mm, 10mm, 12mm
Here is an interesting market research report and forecast about borescope worldwide growth. ​"Borescope Market" 
Articulating Borescopes
Aviation Borescopes
Automotive Borescopes
Industrial Borescopes
Rigid Straight Borescope
UV Borescope
High Temperature Borescopes
Police Borescopes
Thermal Imaging Borescopes
Cleaning Spray Gun
Night Vision Borescopes
Non-Articulation Small Diameter Borescopes

Borescopes Videoscopes