Arduino IDE - Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware...
PlatformIO - Next-generation IDE for IoT
InstaPart - Build circuit boards faster with parts delivered in <24 hrs
Visual Micro - Arduino IDE for Visual Studio and Atmel Studio
embedXcode - embedXcode is a template for Xcode.
UECIDE - Universal Embedded Computing IDE - UECIDE is aiming to be a generic IDE based on the Arduino IDE...