Though definitely not
sexy from a
hacker's perspective,
mainframes running
CICS and
DB2 are the basis of everyday operations of banks and financial institutions, handling billions of transaction per day. In fact, we can easily say that
s/390 machines are built with
CICS /
DB2 performance in mind.
CICS itself acts as a transaction handler, offering a wealth of resources that are usually not matched even on today's so-called application servers, eg WebSphere.
CICS offers 3270 maps (the mainframe screens you see in banks and flight reservation shops) and services, a session handler and unrivaled transaction and disaster recovery capabilities. Also, when you complie a COBOL program, you can embed DB2 SQL in it via CICS, and it gest compiled to a number of really fast to execute low level calls to DB2.
It may not be sexy, and not so fun to program, but it's definitely a workhorse for real-life apps.