IBM i
OS400 (previously referred to as i5/OS) has a new name as of 2 April 2008: IBM i is the operating system that runs on Power Systems hardware (previously called iSeries) and the thing that makes it the unique system it is. See OS/400 101 Introduction.
IBM has created a logo for IBM i: 
IBM i includes a very robust variation of the DB2 database.
Generally, IBM i is accessed using a 5250 emulator.
Contrary to popular belief, IBM i provides a large number of "Open" resources common on other systems, in addition to a few IBM-only 400 languages and database tools.
- Java
- Apache Web server
- Posix compliant API's accessible from many programming languages.
- PHP
Originally OS/400, meaning Operating System 400, was for the AS/400, meaning Advanced System 400.
Then IBM came out with variants and re-inventing renaming ... see Names ... such as the AS/36 Advanced System 36, which offered an advanced version of S/36 OS SSP running on the AS/36 one of two flavors:
