Visual Micro - Arduino IDE for Visual Studio and Atmel Studio
Visuino - Visuino is a visual programming environment that lets you write programs from Arduino circuit boards.
Modkit - Modkit is an open-source programming platform that allows programmers with a variety of backgrounds to share their creations and learn from each other and is allowing programmers to make beautiful software.
XOD - A visual programming language for microcontrollers. Like code, but better.
Embrio - Embrio is an all-in-one open-source visual and real-time development environment built on HTML and JavaScript.
PlatformIO - Next-generation IDE for IoT