Aka: Silicon Graphics Incoporated (former company name) or Silicon Graphics.
A pioneer company founded by Jim Clark, currently selling supercomputers ("Scalable Nodes"), SAN solutions and related products. Their core business used to be rather involving visualization and their software and hardware was (and for a smaller, loyal group of customers: still is) popular among the following industries: energy, government & defense, manufactering, media, science.
SGI acquired a number of companies in its' history including Alias Wavefront (famous because of Maya) and MTI (famous because of the MIPS architecture) and Cray Research (famous because of Cray supercomputers). SGI became famous because of their Indy and [Indigo2] workstations, the Indy competing with Apple, but also because of early supercomputers such as the Onyx. These models are currently not produced anymore, but some are still supported. Newer models exist such as the Origin3000, Onyx3000, Onyx4, Fuel and Tezro. MIPS-based SGI computers come with IRIX, a user-friendly and highly scalable UNIX.
Like other UNIX companies (Sun, SCO) SGI ain't financialy going well as of now. SGI stopped development of the MIPS architecture for the time being and is currently selling and developing Origin-based Altix servers which use the Itanium CPU and the Linux kernel together with other core programs developed in-house. SGI sold Alias in mid-2004. MTI and Cray Research have also been sold, but unlike the Alpha, the MIPS ain't completely "dead". MIPS also makes a wide variety of processors for embedded markets, eg. mobile phones, network routers, games consoles, etc.
SGI supports several FLOSS projects including the Linux kernel, related programs for supercomputers and easy administration, Samba, XFS. XFS is a journaling file system developed for IRIX which SGI has ported to Linux. For a more specific list visit oss.sgi.com