Free42 is a re-implementation of the HP-42S Scientific Programmable Calculator and HP-82240 Printer.
It is a complete rewrite, not using any HP code. It does not require an HP-42S ROM image.
Free42 is an Open Source project. The executables and source code are released under the terms of the GNU General Public License, version 2.

Small as a mouse, fast as a cheetah and available for free. NetSurf is a multi-platform web browser for RISC OS, UNIX-like platforms (including Linux), Mac OS X, and more.

Written by Paul Cantrell.
Video TECO is licensed under the GNU license.

This is the announcement, more details can be found on https://github.com/EtchedPixels/FUZIX
Note that it is not limited to 8-bit processors: core code can be built for 6502, 6809, 68000, 8086, MSP430, pdp11 and Z80/Z180.

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.

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

FlashForth is a Forth stamp system implemented on the Microchip 8-bit PIC18F and 16-bit PIC24, 30, 33 and the Atmel Atmega microcontroller families.

FlashForth also works on the popular Arduino UNO and MEGA boards.

FF (FlashForth) allows you to write and debug complex real-time applications. The complete system including the compiler is executing on the microcontroller.

A Forth interpreter, compiler, assembler, multitasker and user definable interrupts are provided.

A computer with a terminal emulator is used for communicating with FF via a serial or USB link.

This is TexiWeb Jr., a super simple literate programming system built
on top of Texinfo and implemented in awk.

The "tangle" piece was successfully bootstrapped on November 4, 2013.
The "weave" piece started producing a reasonable-looking document
on November 11, 2013.

As of Fri Feb 19 12:07:09 IST 2016, both the source code and literate programming document
are licensed under the GNU GPL. See the file COPYING.

Other repositories from the same author are interesting too: e.g.
the portable C compiler
 https://github.com/arnoldrobbins/pcc-revived
and a converter from RCS to git
 https://github.com/arnoldrobbins/simple-rcs2git

A large quantity of published data is available only in the form of plots and it is often difficult to extract numerical data accurately out of these pictures. There are several softwares available to aid this process, but most are either paid, difficult to use or lack some essential features. Also, many of the existing programs work only on a few specific operating systems and require installation by the user. Most programs only support 2D X-Y plots and so it is not possible to work with polar diagrams, ternary diagrams, microscope images or maps. With these issues in mind, WebPlotDigitizer was developed to be an easy to use, free of charge and opensource program that can work with a variety of plot types and images. This program is developed using HTML5 which allows it to run within a web browser and requires no installation on to the user's hard drive.
Distributed under the GNU General Public License Version 3.

Found on John D. Cook's blog
http://www.johndcook.com/blog/2016/04/20/how-to-digitize-a-graph/

A compact Raspian based distribution
for the Raspberry Pi board computer.