Custom Qt widget plugin interface for Qt Designer

https://www.qt.io/

Qt Designer UI forms support module

https://www.qt.io/

Qt 5 Virtual Keyboard Module

https://www.qt.io/

Qt 5 library for integration of C++/QML with HTML/js clients

https://www.qt.io/

Qt QPA plugin for running an application via a browser using streamed WebGL commands

https://www.qt.io/

Qt implementation of WebSocket protocol

https://www.qt.io/

Qt implementation of WebSocket protocol (QML bindings)

https://www.qt.io/

Qt C++ widgets module

https://www.qt.io/

Qt platform-specific features for X11-based systems

https://www.qt.io/

Qt SAX and DOM implementations

https://www.qt.io/

Qt support for XPath, XQuery, XSLT and XML Schema

https://www.qt.io/

Qt tool wrapper

https://github.com/qt/qtchooser

Tetris like game with multiplayer support

http://code.google.com/p/quadra/

Gnome quadrapassel

https://wiki.gnome.org/Apps/Quadrapassel

Quake III Arena data files

http://www.idsoftware.com/games/quake/quake3-arena/

Command line tool for parsing flash media stream URLs

http://quvi.sourceforge.net/

RabbitMQ is an implementation of AMQP

http://www.rabbitmq.com/

RabbitMQ C AMQP client library

https://github.com/alanxz/rabbitmq-c

Compile regular languages into executable C/C++ code

http://www.complang.org/ragel/

Test performance of storage devices

Elegant sans-serif font, designed in a single thin weight

https://www.theleagueofmoveabletype.com/raleway

Cache and memory benchmarking tool

http://alasir.com/software/ramspeed/

RDF Parser Toolkit for Redland

http://librdf.org/raptor/

RDF Parser Toolkit for Redland

https://librdf.org/raptor/

File archiver (binary port)

https://www.rarlab.com/

OMF help system based on the Freedesktop specification

https://rarian.freedesktop.org/

High-level interface for RDF

http://librdf.org/

Simple window manager with no fat library dependencies

https://www.nongnu.org/ratpoison/

Distributed, collaborative, spam detection and filtering network

http://razor.sourceforge.net/

Unix incarnation of the plan9 shell

http://tobold.org/article/rc

Checks rc scripts for style and common errors

https://github.com/crees/rclint

Version control system (as was in FreeBSD prior to removal)

http://www.gnu.org/software/rcs/

RDP client for Windows NT/2000/2003 Terminal Server

http://www.rdesktop.org/

Fast C++ regex library

https://github.com/google/re2

Lexer generator for C, C++ and Go with a focus on generating fast code

https://re2c.org/

Library for editing command lines as they are typed

https://tiswww.case.edu/php/chet/readline/rltop.html

Build-tool for Erlang that follows OTP principles

https://github.com/rebar/rebar

Converts files between character sets and usages

http://www.gnu.org/software/recode/recode.html

Persistent key-value database with built-in net interface

https://redis.io/

High-level interface for RDF

http://librdf.org

Microsoft .Net Portable Class Library Reference Assemblies

https://blogs.msdn.microsoft.com/dotnet/2013/10/14/portable-class-library-pcl-now-available-on-all-platforms/

Graphical interface to rdesktop

http://gap.nongnu.org/remotedesk/index.html

Fast, secure, efficient backup program

https://restic.github.io

Uncompile an rgb color-name database

https://gitlab.freedesktop.org/xorg/app/rgb

Utility and library for computing and checking of file hashes

http://rhash.sourceforge.net/

Audio player for GNOME

https://wiki.gnome.org/Apps/Rhythmbox

Roboto typeface family

http://developer.android.com/design/style/typography.html

Fully skinnable XHTML/CSS webmail written in PHP

https://roundcube.net/

Convert .rpm files to cpio format

The RPM Package Manager

https://rpm.org/