Tomcat can use the Apache Portable Runtime to provide superior scalability,
performance, and better integration with native server technologies.
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.