Arduino IDE - Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware...
PlatformIO - Next-generation IDE for IoT
MINIBLOQ - miniBloq is an open source graphical programming environment for Multiplo™, Arduino™, physical computing devices and robots.
Visuino - Visuino is a visual programming environment that lets you write programs from Arduino circuit boards.
Arduino Eclipse plugin - Where Arduino meets Eclipse
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.