Exact

Dutch company producing ERP, CRM, HRM, financial, accounting and business software.

Exact for DOS v4.x - v7.x

 *  please note that the mentioned version numbers for these types of files are assumed based on preliminary research since EFS is a proprietary file format. Details follow. (Maurice.de.rooij (talk) 03:59, 16 November 2012 (UTC))

Extensions
A yearbook consists of 3 files:
 * dat: file containing binary data (EFS format ("Exact File System"))), possibly encrypted with at least a username and/or password
 * id: file containing mixed binary and human readable data to identify the yearbook
 * lst: file containing mixed binary and human readable data with fieldnames from the yearbook

Resources

 * Exact products and supported platforms, Office products and database systems
 * Exact for DOS file structure discussion about DAT files (Dutch)