Free communication software

PuTTY () is a free and open-source terminal emulator, serial console and network file transfer application. It supports several network protocols, including SCP, SSH, Telnet, rlogin, and raw socket connection. It can also connect to a serial port. The name "PuTTY" has no official meaning.

The Invisible Internet Project (I2P) is an anonymous network layer (implemented as a mix network) that allows for censorship-resistant, peer-to-peer communication. Anonymous connections are achieved by encrypting the user's traffic (by using end-to-end encryption), and sending it through a volunteer-run network of roughly 55,000 computers distributed around the world. Given the high number of possible paths the traffic can transit, a third party watching a full connection is unlikely. The software that implements this layer is called an "I2P router", and a computer running I2P is called an "I2

open source software implementing a private branch exchange for various Voice over IP protocols

GNOME webcam application

Adium is a free and open-source instant messaging client for macOS that supports multiple IM networks, including XMPP (Jabber), IRC and more. In the past, it has also supported AIM, ICQ, Windows Live Messenger and Yahoo! Messenger. Adium is written using macOS's Cocoa API, and it is released under the GNU GPL-2.0-or-later and many other licenses for components that are distributed with Adium.

distributed protocol for telephony and instant messaging

toolkit for software-defined radios

Remmina is a free and open source remote desktop client for POSIX-based computer operating systems. It supports the Remote Desktop Protocol (RDP), VNC, NX, XDMCP, SPICE, X2Go and SSH protocols and uses FreeRDP as foundation.

software

BitlBee is a cross-platform IRC instant messaging gateway, licensed under the terms of the GNU General Public License.

software

bulletin board system based in Taiwan

thumb|Minicom running a Windows Server 2003 EMS prompt

Fldigi (short for Fast light digital) is a free and open-source program which allows an ordinary computer's sound card to be used as a simple two-way data modem. The software is mostly used by amateur radio operators who connect the microphone and headphone connections of an amateur radio SSB or FM transceiver to the computer's headphone and microphone connections, respectively.

Guvcview (GTK+ UVC Viewer) is a webcam application, i.e. software to handle UVC streams, for the Linux desktop, started by Paulo Assis in 2008. The application is written in C and is free and open-source software released under GPL-2.0-or-later.

H.323 gatekeeper implementation