The Jaxen XPath Engine for Java

Conscrypt is a Java Security Provider that implements parts of the Java Cryptography Extension and Java Secure Socket Extension.

Most popular Mocking framework for unit tests written in Java

Parameterised tests that don't suck

Catch common Java mistakes as compile-time errors

A programmer-oriented testing framework for Java.

Google Core Libraries for Java 6+

Better GWT unit testing

Java (and original) version of Hamcrest