CICS/FEPI

What is FEPI?
FEPI stands for Front End Programming Interface. It is a terminal emulator implemented via a Programming Interface. FEPI is integrated into CICS, so if you have CICS (CICS/ESA V3.3 or above) then you already have access to FEPI. FEPI can communicate with transactions running on CICS or IMS systems.

What can I do with FEPI?
FEPI can be used to integrate your existing CICS applications into one system without needing to alter the existing systems.
 For example if two companies merge, FEPI can be used to provide a single user interface to both of the merged companies' systems. Another example, if you want to be able to access all a customer's details from a number of different systems in one single system - you could have a single screen where the user enters the customer's name and the FEPI interface will go to, for example, the Home Insurance system, the Motor Insurance system and Accounts system retrieve details from each of these systems. The information from each of these different systems will be returned and be available for displaying on one screen. This could be useful, for example, for cross selling. You might be able to see that a customer has Motor Insurance, but not Home Insurance, you could then ask the customer if they had considered buying your company's Home Insurance product!
You could also use FEPI to add new functions to a system. Say you want to keep an existing system stable, but want to add new functionality, you could write a program which would use FEPI to access the stable system, and access the programs which contain the new functionality when it is required.
As part of your company's Web enablement you could use FEPI to provide an interface between your CICS systems and your Web site. You could keep the existing CICS systems, but have a FEPI based system to handle enquiries from the Web. The FEPI programs would extract the required information from the existing system and return it to the Web server.
 

Further Reading
CICS Front End Programming Interface User's Guide (IBM SC33-1629-02)
The CICS Programmer's Guide to FEPI (McGraw Hill ISBN 0-07-7077793-8)