Apache HTrace is an Apache Incubator project providing an open source framework for distributed tracing. It can be used with both standalone applications and libraries.
HTrace was designed for use in big distributed systems such as the Apache Hadoop Distributed Filesystem and the Apache HBase storage engine. However, there is nothing Hadoop-specific about HTrace. It has no dependencies on Hadoop, and is a useful building block for many distributed systems. See the developer guide for information on adding HTrace support.
The API documentation for htrace-core is online.