There are an endless number of specialty connectors on the market. Many of the specialty connectors are proprietary in nature, and most have very limited functionality. Most specialty connectors are designed for only one specific application.
This connector is very similar to the 50-pin Centronics interface. The biggest difference is that the RJ21 connector uses screws to anchor into place instead of bail locks. Sometimes, it is called a "Champ" connector (referencing a series of connectors made by Amp), or an "Amphenol" connector (referencing the connector manufacturer). RJ21 interfaces are typically used for datacomm trunking applications.
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This is a special type of D-Sub connector. It contains 10 standard DB-style pins, and 3 coaxial pins. This interface is often used for Sun/SGI workstation video applications. The gender of a 13W3 connector is determined by its 10 DB-style pins, not its coaxial pins (which are opposite in gender). For example, a male 13W3 plug has male DB pins, and female coaxial pins.
IEEE-488 is a standard for communication widely used with testing/measurement devices and instruments. The technology was developed by Hewlett-Packard back in the 1970s, and was called HP-IB (Hewlett-Packard Instrument Bus). It was then widely adopted in the industry, and codified into IEEE-488. It is also referred to as GP-IB (General Purpose Interface Bus). The physical interfaces used by IEEE-488 assemblies are 24-pin Centronics connectors. Most cables are "stackable"; they have both male and female connections built into a single connector shell.
This is a relatively large, unique connector used in Token Ring networking applications. Before ethernet's rise to prominence, Token Ring was a local networking architecture that was developed and promoted by IBM® in the 1980s. The Data Connector used by Token Ring cables is hermaphroditic; it does not have separate male or female versions. All IBM data connectors can plug into each other.
This is a blocky connector with large pins and sockets, used often for datacomm modem applications. The nickname "Winchester" probably comes from Winchester Electronics, a connector manufacturer based in Connecticut. A V.35 connector has 34 pin positions, and often several of these positions are left unloaded.