Quasar
Fibers, channels and actors for the JVM
...Quasar is developed by Parallel Universe and released as free software, dual-licensed under the Eclipse Public License and the GNU Lesser General Public License. Quasar fibers rely on bytecode instrumentation. This can be done at classloading time via a Java Agent, or at compilation time with an Ant task. Quasar’s lightweight thread implementation relies on bytecode instrumentation. Instrumentation can be performed at compilation time or at runtime using a Java agent. The easy and preferable way to instrument programs using Quasar is with the Java agent, which instruments code at runtime. ...