Daily maps of navigation accuracy as reported by aircraft using ADS-B.
Provided by John Wiseman

Experiments tracking DCF77 and MSF, using amplitude, phase and correlation to measure time with respect to GPS.

M1GEO's blog, found https://www.george-smart.co.uk/projects/lnb-bias-tee/ when looking for bias tees.
Another air quality sensor is described on https://www.george-smart.co.uk/2021/02/an-esp8266-based-air-quality-sensor/

We currently support the processing of:

the United States' Global Positioning System (GPS);
the Russian GLONASS system (GLONASS);
the European Union's Galileo system (Galileo);
the Chinese Navigation Satellite System (BeiDou);
the Japanese QZSS develop system (QZSS).
We are actively developing Ginan to have the following capabilities and features:

Precise Orbit & Clock determination of GNSS satellites (GNSS POD);
Precise Point Positioning (PPP) of GNSS stations in network and individual mode;
Real-Time corrections for PPP users;
Analyse full, single and multi-frequency, multi-GNSS data;
Delivering atmospheric products such as ionosphere and troposphere models;
Servicing a wide range of users and receiver types;
Delivering outputs usable and accessible by non-experts;
Providing both a real-time and off-line processing capability;
Delivering both position and integrity information;
Routinely produce IGS final, rapid, ultra-rapid and real-time (RT) products;
Model Ocean Tide Loading (OTL) displacements.
The software consists of two main components: Network Parameter Estimation Algorithm (PEA) and Precise Orbit Determination (POD).

Peregrine is a fast and flexible open-source software GNSS receiver. It can be used as a standalone application to post-process GNSS data all the way to PVT solutions or as from within IPython as a toolkit for GNSS data exploration.

Peregrine is written in Python for flexibility and ease of development and uses the libswiftnav C library for speed.

Full documentation available online at http://docs.swift-nav.com/peregrine

Found via https://github.com/odrisci/gnss-sdr, a fork of GNSS-SDR implementing code-less tracking for Galileo E1 PRS signals, which in turn was found in "Codeless Code Tracking of BOC Signals" by Cillian O’Driscoll, James T. Curran; Proceedings of the 29th International Technical Meeting of the ION Satellite Division, ION GNSS+ 2016, Portland, Oregon, September 12-16, 2016, pp. 497-508.

Portable C libraries which provide APIs to build applications with u-blox products and services. Delivered as add-on to existing microcontroller and RTOS SDKs.
Found on https://www.spezial.com/de/node/2052

Found on Leah Neukirchen's blog https://leahneukirchen.org/trivium/2021-09-19

See also https://zee-nix.blogspot.com/2017/05/introducing-gps-share.html and https://github.com/zeenix/gps-share
gps-share is a utility to share your GPS device on local network. It has two goals:

Share your GPS device on the local network so that all machines in your home or office can make use of it.
Enable support for standalone (i-e not part of a cellular modem) GPS devices in Geoclue. Since Geoclue has been able to make use of network NMEA sources since 2015, gps-share works out of the box with Geoclue.

The latter means that it is a replacement for GPSD and Gypsy. While "why not GPSD?" has already been documented, Gypsy has been unmaintained for many years now. I did not feel like reviving a dead project and I really wanted to code in Rust language so I decided to create gps-share.

Details about outages in the global positioning system (GPS).

GNSS Positioning Performance Monitor.