Monocypher is an easy to use crypto library inspired by libsodium and TweetNaCl.

Given a version number MAJOR.MINOR.PATCH, increment the:

   MAJOR version when you make incompatible API changes,
   MINOR version when you add functionality in a backwards-compatible manner, and
   PATCH version when you make backwards-compatible bug fixes.

Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format.

Logic simulator with graphical entry, written in C# and released under the GPL.
Work in progress, a followup of http://www.cburch.com/logisim/, which is written in Java.

Cryptocat is free software with a simple mission: everyone should be able to chat with their friends in privacy.

   Open source. All Cryptocat software is published transparently.
   Encrypted by default. Every message is encrypted, always.
   Forward secure. Chats are safe even if your keys are stolen.
   Multiple devices. Devices receive messages even when offline.
   File sharing. Securely share files with friends.

Available for Windows, Linux and Mac.

PDF Tools is, among other things, a replacement of DocView for PDF files. The key difference is, that pages are not pre-rendered by e.g. ghostscript and stored in the file-system, but rather created on-demand and stored in memory.

This rendering is performed by a special library named, for whatever reason, poppler, running inside a server program. This program is called epdfinfo and its job is it to successively read requests from Emacs and produce the proper results, i.e. the PNG image of a PDF page.

Actually, displaying PDF files is just one part of PDF Tools. Since poppler can provide us with all kinds of information about a document and is also able to modify it, there is a lot more we can do with it.

[shaarli save link does not work here under Firefox 45.5.1/Windows or Firefox 51.0.1 (64-bit) on xubuntu, because github does not allow "foreign" JavaScript]

spigot is a calculating program. It supports the usual arithmetic operations, square and cube roots, trigonometric and exponential functions, and a few other special functions such as erf.

spigot differs from the average calculating program in that it is an exact real calculator. This means that it does not suffer from rounding errors; in principle, it can keep generating more and more digits of the number you asked for until it runs out of memory.

In particular, if you ask for a complex expression such as sin(sqrt(pi)), then most calculating systems would compute first pi, then sqrt(pi) and finally sin(sqrt(pi)), accumulating a rounding error at each step, so that the final result had a build-up of error and you would have to do some additional error analysis to decide how much of the output you could trust.

spigot, on the other hand, does not output any digit until it is sure that digit is correct, so if you ask for (say) 100 digits of sin(sqrt(pi)) then you can be sure they are the right 100 digits.

Apart from the Scheme compiler Chicken
 http://www.call-cc.org/
two other Scheme and one Forth system, there is
 MA, a minimalistic variant of the Acme editor, written in Tcl/Tk.

sshguard protects hosts from brute-force attacks against SSH and other services. It aggregates system logs and blocks repeat offenders using one of several firewall backends, including iptables, ipfw, and pf.

GNSS signal processing functions written in C
       Code generations
       Signal acquisition / tracking
       Decoding navigation messages
       Pseudo-range / carrier phase mesurements
   GUI application (AP) written in C++/CLI
   Visualization of GNSS signal processing in real-time
   Real-time positioning with RTKLIB (http://www.rtklib.com/)
   Observation data can be outputted in RINEX or RTCM format
   Support following signals (tracking and decoding navigation message)
       GPS L1CA
       GLONASS G1
       Galileo E1B
       BeiDou B1I
       QZSS L1CA/SAIF/LEX
       SBAS L1
   Support following front-ends for real-time positioning
       NSL Stereo http://www.nsl.eu.com/primo.html
       SiGe GN3S sampler v2/v3 https://www.sparkfun.com/products/10981
       Nuand BladeRF http://nuand.com/
       RTL-SDR http://sdr.osmocom.org/trac/wiki/rtl-sdr
   Support RF binary file for post processing

Mentioned on https://www.rtl-sdr.com/receiving-gps-with-an-rtl-sdr-dongle-and-gps-antenna/

A GNU implementation of the Secure Shell protocols

lsh is a free implementation (in the GNU sense) of the ssh version 2 protocol, standardised by the IETF SECSH working group.