Tomcat can use the Apache Portable Runtime to provide superior scalability,
performance, and better integration with native server technologies.
The Apache Portable Runtime is a highly portable library that is at the
heart of Apache HTTP Server 2.x. APR has many uses, including access to
advanced IO functionality (such as sendfile, epoll and OpenSSL), OS level
functionality (random number generation, system status, etc), and native
process handling (shared memory, NT pipes and Unix sockets).
These features allows making Tomcat a general purpose webserver, will
enable much better integration with other native web technologies, and
overall make Java much more viable as a full fledged webserver platform
rather than simply a backend focused technology.