Arduino IDE - Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware...
PlatformIO - Next-generation IDE for IoT
Arduino - Build your own electronics
Visuino - Visuino is a visual programming environment that lets you write programs from Arduino circuit boards.
XOD - A visual programming language for microcontrollers. Like code, but better.
MINIBLOQ - miniBloq is an open source graphical programming environment for Multiplo™, Arduino™, physical computing devices and robots.