What is the difference between OctoPrint and OctoPi? Are they the same thing?



No, OctoPrint and OctoPi are not the same thing.

OctoPrint is a fully featured print server/web interface for 3D printers, written in Python and HTML/JS. It is platform agnostic and runs basically everywhere where you can install Python 2.7, be it a cheap single PCB computer like the Raspberry Pi running Linux, a fully featured gaming PC running Windows, a Mac running MacOSX or a server running some BSD flavor. It was created and is actively maintained by Gina Häußge aka @foosel.

OctoPi on the other hand is a preconfigured image for the Raspberry Pi. It is based on the Raspbian Lite image by the Raspberry Pi Foundation and bundles OctoPrint plus mjpg-streamer as a webcam server plus CuraEngine plus a couple of scripts to make your life easier and allow for easy initial setup. This image is probably the most common form of running OctoPrint. It was created and is actively maintained by Guy Sheffer aka @guysoft.

Think of it this way: OctoPi is more or less the operating system, OctoPrint is the main application that runs on it and actually talks to your printer.

Current versions:

Raspberry pi 3 model a+
Will PrusaPrint work with an external raspberry pi on a prusa i3 MK3
New OctoPi Release: 0.16.0
OctoPrint failing to update to 1.3.10
OctoPi WiFi/network connection troubleshooting megatopic
ERROR: tornado.access - WARNING - 404 GET /currentsetting.htm
Setting up OctoPrint on Windows
Raspian and Octoprint together on USB storage device
OctoPrint with PiCam V2
Can octoprint os runs on odroid C2?
Webcam not accessible from OctoPi