The FGI-GSRx software receiver has been extensively used as a research platform for the last one decade in different national and international Research and Development (R&D) projects to develop, test and validate novel receiver processing algorithms for robust, resilient and precise Position, Navigation and Timing (PNT). At present, the FGI-GSRx can process GNSS signals from multiple constellations, including GPS, Galileo, BeiDou, GLONASS, and NavIC. The software receiver is intended to process raw Intermediate Frequency (IF) signals in post-processing. The processing chain of the software receiver consists of GNSS signal acquisition, code and carrier tracking, decoding the navigation message, pseudorange estimation, and Position, Velocity, and Timing (PVT) estimation. The software architecture is built in such a way that any new algorithm can be developed and tested at any stage in the receiver processing chain without requiring significant changes to the original codes.

Reference points in Austria where the accuracy of GNSS receivers can be checked.

Sean Barbeau is the author of GPSTest, which has a Google group
https://groups.google.com/g/gpstest_android
See also https://bit.ly/gpstest-device-database for the GPSTest Database and
https://github.com/barbeau/awesome-gnss
for a collection of links to open source GNSS software

Blog article describing the calculation of the impact location of the DSLWP-B spacecraft.
See also
https://destevez.net/2019/09/ephemeris-quality-during-the-galileo-outage/
where he analysed the Ephemeris quality during the Galileo outage in July 2019.

An open source Global Navigation Satellite Systems software-defined receiver.
Based on GNU radio.

The Android Framework provides access to raw GNSS measurements on several Android devices (Android 7 or higher is needed).

Exploring precision GPS/GNSS with RTKLIB open source software and low-cost u-blox GPS receivers.
This particular post links to the announcement of the u-blox ZED-F9P high precision GNSS module
https://www.u-blox.com/en/product/zed-f9p-module
According to https://forum.u-blox.com/index.php/18878/when-can-i-get-a-zed-f9p
"I contacted u-blox and they said that the evaluation kits will be available at the end of Nov 2018."

The uBlox LEA-6T supports precision GPS timing for demanding positioning applications such as basestations. It features a time mode function whereby the GPS receiver assumes a stationary 3D position, whether programmed manually or determined by an initial self-survey. Stationary operation enables GPS timing with only one visible satellite and eliminates timing errors which otherwise result in positioning errors. An accuracy of up to 15 ns is achievable by using the quantization error information to compensate the granularity of the time pulse. A built-in time mark and counter unit provide precise time measurement of external event inputs