Zabbix/J is a framework for integrating Zabbix monitoring into Java applications. Zabbix is an "enterprise-class Open Source distributed monitoring solution" which provides telemetry and triggers across entire infrastructures. Zabbix/J makes it simple to expose metrics from your Java applications, giving them visibility as first class citizens in a Zabbix configuration.
jmxtrans is effectively the missing connector between JMX and whatever logging or graphing package that you can dream up. jmxtrans is very powerful tool that reads JSON configuration files specifying servers/ports and JMX domains/attributes and then outputs the data in whatever format you want via special "Writer" objects that you can code up yourself. It does this with a very efficient engine design that will scale to querying literally thousands of machines. The core engine is pretty solid and writers are included for cacti/rrdtool, graphite, and stdout.
Yap4j is the simplest library for parsing CSV files in Java. It deserializes CSV files into a list of POJOs using a set of Java annotations, while allowing you to specify Object-CSV mappings. It automatically converts to and from a wide range of data types, and includes support for types from popular libraries such as Joda Time, and support for custom record delimiters.
kongcurrent provides an easy-to use helper to assist debugging issues which cause exceptions under concurrent access. It was inspired by a problem in which a non-thread-safe Map object held by a third party framework was accidentally shared between threads, causing a ConcurrentModificationException. The helper (a "monitor") creates a proxied version of an object implementing some interface. The proxy can track invocations of the objects' methods and can report on potential concurrent access on the object. This can be used to help find code paths which concurrently access the object through its interface methods. By design, the helper is extensible, and can be adapted to more specific needs.