1985: AmigaOS - History of Desktop OSs
Commodore released its Amiga 1000 in 1985 with a heavy focus on multimedia applications, including music production, graphic design and desktop publishing, video editing, as well as video gaming. The proprietary AmigaOS was built on a kernel with preemptive multitasking features and was usually used via the GUI called Workbench.
AmigaOS is still maintained today. However, the software responsibility transitioned from Commodore after the company's demise to Haage&Partner in 1994 and to Hyperion Entertainment in 2001. The latest stable version is AmigaOS 4.1 Update 5, released in August 2012.(Image courtesy of OSNews.com)