Mail client with tons of features, customization chances, support for IMAP, POP3, multiple storage formats.

Mailboxes synchronization tool; allows to download email locally; MailDir format supported.

MUA written in Python using the NotMuch backend; MailDir format support.

Mail client which aims at being "fast, easy to use email client that is suitable for both the inexperienced email user as well as for the most demanding of power users".

"The Mutt of RSS Feed Readers": Newsbeuter is an open-source RSS/Atom feed reader for text terminals. It runs on Linux, FreeBSD, Mac OS X and other Unix-like operating systems. Newsbeuter's great configurability and vast number of features make it a perfect choice for people that need a slick and fast feed reader that can be completely controlled via keyboard.

Custom SSH server written in Go. Instead of a shell, you get a chat prompt

A "fast, light and extensible chat client". WeeChat is a fast, light and extensible chat client, with a text-based user interface. WeeChat is: - modular: a lightweight core with optional plugins - multi-protocols architecture (mainly IRC) - multi-platforms: Linux, Unix, BSD, GNU Hurd, Haiku, macOS and Windows (Bash/Ubuntu and Cygwin). - extensible with C, Python, Perl, Ruby, Lua, Tcl, Scheme, Javascript and PHP - fully documented and translated into several languages - a free program released under the terms of the GNU General Public License version 3 - an active project with a large community for scripts.

Twitter client for the terminal; allows almost all the operations that can be done from GUI and Web clients

The most popular IRC client for the command-line; a flexible program, with many options and supporting many protocols

IM program supporting many protocols, including Yahoo!, AIM, IRC, or WLM; comes with the Pidgin project

The best CLI client for Slack, because everything is terrible!

Telegram client on your terminal.

Downloads videos from YouTube and some other sites; useful for automated bulk downloads.

aims to be a "easy-to-use and unbloated client for the UNIX and UNIX-like console".

Synchronizes a local copy of a website with a remote copy on a server; does not use SSH/scp but FTP for file copy; useful when the remote server does not support secure copy.

Mirror directories across networked machines; handles diffs/changed files; works across SSH; plenty of parameters.

"An open source tool that lets you securely and anonymously share a file of any size."

The program allows transfer arbitrary-sized files and directories (or short pieces of text) from one computer to another.

The two endpoints are identified by using identical human-readable codes.

"Sophisticated ftp/http client, and a file transfer program supporting a number of network protocols"; support for bookmarks and mirroring features.

A lightweight, Free Software, cross-platform BitTorrent client; a terminal curses interface, web interface and command line client can connect to a running daemon to manage torrent downloads.