Moquette is a Java implementation of an MQTT 3.1 broker. Its code base is small. At its core, Moquette is an events processor; this lets the code base be simple, avoiding thread sharing issues.
Eclipse Californium (Cf) is an open source implementation of the Constrained Application Protocol (CoAP). It is written in Java and targets unconstrained environments such as back-end service infrastructures (e.g., proxies, resource directories, or cloud services) and less constrained environments such as embedded devices running Linux (e.g., smart home/factory controllers or cellular gateways).
The OM2M project is an open source implementation of the oneM2M standard. It provides a framework for developing services independently of the underlying network and aims to facilitate deployment of vertical applications and heterogeneous devices.
Kura offers a Java/OSGi-based container for M2M applications running in service gateways. Kura provides or, when available, aggregates open source implementations for the most common services needed by M2M applications. Kura components are designed as configurable OSGi Declarative Service exposing service API and raising events. While several Kura components are in pure Java, others are invoked through JNI and have a dependency on the Linux operating system.
The Plug-in Development Environment project and Web Tools Platform project provide plenty of tools for OSGi development and Java EE development, respectively.
