Arduino IDE - Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware...
PlatformIO - Next-generation IDE for IoT
Arduino Eclipse plugin - Where Arduino meets Eclipse
XOD - A visual programming language for microcontrollers. Like code, but better.
UECIDE - Universal Embedded Computing IDE - UECIDE is aiming to be a generic IDE based on the Arduino IDE...
MINIBLOQ - miniBloq is an open source graphical programming environment for Multiplo™, Arduino™, physical computing devices and robots.