Gateway
Device sitting at a network node for interfacing with another network that uses different protocols. Works on OSI layers 4 to 7.

Router
A specialized network device that determines the next network point to which to forward a data packet toward its destination. Unlike a gateway, it cannot interface different protocols. Works on OSI layer 3.

Bridge
A device that connects multiple network segments along the data link layer. Works on OSI layer 2.

Computer Switch
In computer software, specifically command line interfaces, a switch (also known as option, command-line parameter, or command-line argument) is an indication by a user that a computer program should change its default behaviour.

Network Switch
A device that allocates traffic from one network segment to certain lines (intended destination(s)) which connect the segment to another network segment. So unlike a hub a switch splits the network traffic and sends it to different destinations rather than to all systems on the network. Works on OSI layer 2.

Ethernet Hub
Connects multiple Ethernet segments together making them act as a single segment. When using a hub, every attached device shares the same broadcast domain and the same collision domain. Therefore, only one computer connected to the hub is able to transmit at a time. Depending on the network topology, the hub provides a basic level 1 OSI model connection among the network objects (workstations, servers, etc). It provides bandwidth which is shared among all the objects, compared to switches, which provide a dedicated connection between individual nodes. Works on OSI layer 1.

Repeater
Device to amplify or regenerate digital signals received while setting them from one part of a network into another. Works on OSI layer 1.

Multilayer Switch
A switch which, in addition to switching on OSI layer 2, provides functionality at higher protocol layers.

Protocol Converter
A hardware device that converts between two different types of transmissions, such as asynchronous and synchronous transmissions.

Media Hub
Connects a computer network to a home theatre

Proxy
Computer network service which allows clients to make indirect network connections to other network services

Firewall
A piece of hardware or software put on the network to prevent some communications forbidden by the network policy

Multiplexer
Device that combines several electrical signals into a single signal

Network Interface Card
A piece of computer hardware to allow the attached computer to communicate by network

Modem
Device that modulates an analog "carrier" signal (such as sound), to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information, as a computer communicating with another computer over the telephone network

ISDN Terminal Adapter
A specialized gateway for ISDN

Line Driver
A device to increase transmission distance by amplifying the signal. Base-band networks only.