Roughtime is a protocol that aims to achieve rough time synchronisation in a secure way that doesn't depend on any particular time server, and in such a way that, if a time server does misbehave, clients end up with cryptographic proof of it.

“Rough” time synchronisation means that, at this stage, we would be happy with time synchronisation to within 10 seconds of the correct time. If you have serious time synchronisation needs you‘ll want the machinery in NTP or even PTP (which needs hardware support to do right). There’s no reason why Roughtime shouldn‘t be (almost) as precise as NTP, but the use cases that we have in mind for now don’t need much precision. For example, about 25% of certificate errors shown by Chrome appear to be caused by bad local clocks and we don't need much precision to fix that.

Found via Cillian O'Driscoll's fork https://github.com/odrisci/roughtime
See also https://github.com/oreparaz/vroughtime for a simple client written in C.

See also https://time.is which measures the error of your computer's clock.

Precise timing related network testing tools: isoping, isostream, udpstress.

clockspeed uses a hardware tick counter to compensate for a persistently fast or slow system clock. Given a few time measurements from a reliable source, it computes and then eliminates the clock skew.

sntpclock checks another system's NTP clock, and prints the results in a format suitable for input to clockspeed. sntpclock is the simplest available NTP/SNTP client.

taiclock and taiclockd form an even simpler alternative to SNTP. They are suitable for precise time synchronization over a local area network, without the hassles and potential security problems of an NTP server.

An experimental implementation of tlsdate (https://github.com/ioerror/tlsdate) in Go.
WARNING: This software has not been reviewed. You probably shouldn't use it.

The TAPR TICC is a two-channel timestamping counter with better than 60 picosecond resolution and less than 100 picosecond typical jitter. It has an Allan Deviation noise floor below 1x10-10 for a one second measurement.

The entire desire to do this came about from reading about building a Stratum 1 clock using a Raspberry PI at http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html and from the use of a Sony radio clock to provide WWVB pulses from the WWVB receiver module that was used in the radio clock.

However, all of the projects and examples I found used Linux which I did not really want to use. I much preferred to use NetBSD, but it lacked a number of critical features that would be required to make a properly working Stratum 1 clock. Interrupt support for the GPIO pins was needed and adding a PPSAPI driver that could be triggered by a GPIO interrupt would be necessary.

WaveDrom draws your Timing Diagram or Waveform from simple textual description.
It comes with description language, rendering engine and the editor.
WaveDrom editor works in the browser or can be installed on your system.
Rendering engine can be embeded into any webpage.

Leap second observations, long wave receivers for NTP.