Californium (Cf)

Californium (Cf) is a powerful CoAP framework targetting back-end services and stronger Internet of Things devices. It provides a convenient API for RESTful Web services that support all of CoAP's features. Californium has an extremely scalable architecture and outperforms high-performance HTTP servers. CoAP's low overhead allows to handle millions of IoT devices with a single service instance. The flexible concurrency model allows to implement whatever is best for your application. Californium has been running code for the IETF and is passing all ETSI Plugtest test specifications. https://eclipse.org/californium/

Erbium (Er)

Erbium (Er) is a low-power REST Engine for the Contiki OS (http://www.contiki-os.org/). The REST Engine includes a comprehensive embedded CoAP implementation, which became the official one for the Contiki OS. It supports RFC 7252 together with blockwise transfers and observing. This CoAP C implementation was successfully tested at the ETSI IoT CoAP Plugtests in Paris, France, March 2012 and Sophia Antipolis, France, November 2012. It passed all mandatory and optional tests with all the other implementations that supported them. Erbium is also used to implement the IPSO Profile and tested at the IPSO Interop Event in Paris, France, April 2012. http://people.inf.ethz.ch/mkovatsc/erbium.php

mjCoAP

mjCoAP is an open source lightweight Java-based implementation of CoAP, which aims at simplifying the development of CoAP-based IoT applications. The mjCoAP library has been developed in the University of Parma and is fully RFC-compliant. Moreover, it integrates several IETF CoRE WG specifications, such as blockwise transfers, resource observing, and HTTP/CoAP mapping. mjCoAP

Contiki

Contiki is an open source operating system for the Internet of Things. Contiki connects tiny low-cost, low-power microcontrollers to the Internet. Contiki supports fully standard IPv6 and IPv4, along with the recent low-power wireless standards: 6lowpan, RPL, CoAP. Contiki applications are written in standard C, with the Cooja simulator Contiki networks can be emulated before burned into hardware. Contiki is developed by a world-wide team of developers with contributions from Atmel, Cisco, ETH, Redwire LLC, SAP, Thingsquare, and many others, led by Adam Dunkels of Thingsquare. http://www.contiki-os.org/index.html