This is a repository for good Arduino boards and libraries with links.
Arduino IDE Download here
They also produce some good introduction tutorials and content. Don’t forget that there are a lot of example sketches that come with the Arduino IDE and most libraries you install. These can be found under the “File” menu.
List of boards to add to Arduino:
ESP8266 based boards e.g. Node MCU v1.0 & Arduino wifi clone boards
STM32 based board support
ESP32 based board support
Additional AVR/Atmel mcu support e.g. ATMEGA1284
Add be adding these links (each on a new line) to the ‘File > Preferences > Additional boards manager URLs’ input
List of good libraries for Arduino projects: