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/

Round Robin Database Tools

http://www.rrdtool.org/

Fast spam filtering system

https://rspamd.com/

Restricted Secure SHell only for sftp or/and scp

http://www.pizzashack.org/rssh/index.shtml

Network file distribution/synchronization utility

http://rsync.samba.org/

RTMP streams download utility

http://rtmpdump.mplayerhq.hu/

BitTorrent Client written in C++

https://github.com/rakshasa/rtorrent

Ruby interface to Oracle Berkeley DB revision 2 or later

https://github.com/knu/ruby-bdb

Binary data dumper module for Ruby

http://www.geocities.co.jp/SiliconValley-Oakland/2986/

Package management framework for the Ruby language

https://rubygems.org/

Object-oriented interpreted scripting language

https://www.ruby-lang.org/en/

Object-oriented interpreted scripting language

https://www.ruby-lang.org/en/

Fast, open source text processor and publishing toolchain

https://asciidoctor.org/

Fast, Enjoyable HTML Parser for Ruby

https://github.com/hpricot/hpricot

Framework-agnostic way to render logic-free views

https://github.com/mustache/mustache

Fast Markdown converter for ruby based on discount

https://dafoster.net/projects/rdiscount/

RDoc produces HTML and command-line documentation for Ruby projects

https://ruby.github.io/rdoc/

Builds manuals

https://rtomayko.github.io/ronn/

Restricted User SHell, providing limited remote access to resources

https://puszcza.gnu.org.ua/software/rush/

Language with a focus on memory safety and concurrency (FreeBSD version)

https://www.rust-lang.org/

Clone of the terminal emulator rxvt modified to support Unicode

http://software.schmorp.de/pkg/rxvt-unicode.html

Subset of a well-known texture compression scheme

https://github.com/divVerent/s2tc/wiki

nsupdate utility with the GSS-TSIG support

https://www.isc.org/software/bind

Free SMB/CIFS and AD/DC server and client for Unix

https://www.samba.org/

API for access to scanners, digitals camera, frame grabbers etc

http://www.sane-project.org/

Stand-Alone shell combining many common utilities

http://members.tip.net.au/~dbell/

Wrapper around libsass

http://libsass.org/

Scala Programming Language

http://www.scala-lang.org/

Scan_ffs recovers lost disklabel

High-speed Dirac codec

http://www.diracvideo.org/

ANSI C version of the SciMark2 benchmark

https://math.nist.gov/scimark2/download_c.html

Build tool alternative to make

https://scons.org/

Tiny shell that only permits scp and sftp

https://github.com/scponly/scponly/wiki

Converts the output of "vidcontrol -p" to PNG

Converts the output of "vidcontrol -p" to text

Multi-screen window manager

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

Small and lightweight screen(1) wrapper

https://sourceforge.net/projects/screenie/