The original multitasking operating system that NeXT, Inc. developed to run on its proprietary NeXT computers (informally known as "black boxes"). NEXTSTEP includes a specific graphical user interface, an interface builder, object-oriented application builder, and several "kits" of prebuilt software objects such as the Indexing Kit for databases. This software runs on top of NeXT's version of the Mach operating system on NeXT, 486, Pentium, HP-PA, and Sun SPARC computers. The official spelling changed from "NeXTstep" to "NeXTStep" to "NeXTSTEP", and finally "NEXTSTEP". The last release of NEXTSTEP was 3.3, which NeXT then developed into "OpenStep". See also: GNUStep.