OpenTag is an open-source RTOS that implements the DASH7 standard for wireless sensor networking and M2M comms.
DASH7 is a wireless standard that was borne out of the US Military, and it is designed for extreme low-power and low-latency wireless communication, so it is great for communication between moving things or for anything that can benefit from a lower power requirement. DASH7 is also designed to finally eliminate "Application Profiles" as it introduces a filesystem and data methodology not available to any other WSN/M2M/IoT standard. Most DASH7 devices can be re-mapped over-the-air to take-on vastly different applications (sort of like the scene in "The Matrix" where Trinity learns to fly a helicopter).
OpenTag was created and is maintained by JP Norair. Norair also invented DASH7 during the same time, so there is a high degree of synergy between the standard and the implementation. Do not be fooled by the small size: OpenTag is a full-featured, real-time exokernel with a large API and library. It is capable of communicating with native DASH7 peers as well as UDP, SCTP, and NDEF connections.
OpenTag is designed to run on low-power microcontrollers. On the MSP430, a typical endpoint project might require 16-24KB ROM (Flash) and 1-2KB RAM. For gateway or router projects, a typical project MSP430 project is 20-32KB ROM and 2-4KB RAM. Cortex M projects are typically about 12% larger. Officially, there is no roadmap to support non-MSP430 or non-Cortex-M microcontrollers, but OpenTag is very portable, and there are community projects to port to, at least, AVR8 and PIC24.
This is the OpenTag Mainline Distribution. It is maintained by JP Norair, the creator of OpenTag and inventor of the DASH7 wireless specification. The Haystack Distribution of OpenTag (HDO) is a contributory distribution of this distribution. (http://www.haystacktechnologies.com)
Indigresso Wiki: http://www.indigresso.com/wiki/doku.php
Indigresso Forum: http://www.indigresso.com/forum/
Haystack Technologies: http://www.haystacktechnologies.com
OpenTag uses the OpenTag License, which is an open source license similar to ClearBSD, Analog Devices BSD, and some others. You can read about the OpenTag License on the Indigresso Wiki or on this GitHub project Wiki.