Source and binaries for (among others) 64 bit Windows can be found on https://github.com/debauchee/barrier/

Xpra is an open-source multi-platform persistent remote display server and client for forwarding applications and desktop screens.
It gives you remote access to individual applications or full desktops.
On X11, it is also known as screen for X11: it allows you to run programs, usually on a remote host, direct their display to your local machine, and then to disconnect from these programs and reconnect from the same or another machine, without losing any state.
It can also be used to forward full desktops, from X11 servers, MS Windows, or Mac OS X.

Xpra also allows forwarding of sound, clipboard and printing services.
Sessions can be accessed over SSH, or password protected over plain TCP sockets with or without SSL.
Xpra is usable over reasonably slow links and does its best to adapt to changing network bandwidth constraints.

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