[zargon]

Teensies range from 16 MHz AVR chips to this 600 MHz Cortex M7. Arduinos cover a variety of platforms as well. ESP32 is if you want WiFi integrated. Raspberry Pi is a full blown computer. This is a full gamut of capability. What you choose for a project depends on your requirements.

Automatic window blind opener? Teensy 2.0 if you like AVR, Teensy LC if you like ARM.

Camera watching your 3d printer using computer vision to detect if it catches on fire? Raspberry Pi.

[TaylorAlexander]

The Raspberry Pi Zero W is great for tasks that need wifi too (window blinds, etc). At $10 it's cheap and it's really nice to write your programs in python. I've got plenty of experience with microcontrollers and C++ but I find python just so much nicer to use when I can. You can even host a web page from it for a quick and easy GUI control (use Flask for a pure python implementation).