There's been mention of timestamping in this thread. Those of us that
work with GPS and precise clocks use it a lot. Time stamping, sometimes
called time tagging, has advantages over traditional period / frequency
counters or time interval counters.
Most any microcontroller can be used to collect time stamps;
microprocessors with GPIO pins as well. It's easy to get resolution
ranging from 100 ns (10 MHz clock) to 1 ns (1 GHz clock).
There are several laboratory-grade instruments that do timestamping to
tens of ps. Look for the Keysight 53230A, or the Stanford Research
FS740, or the Pendulum CNT-91. All of these are high-performance
universal counters, with lots of features, including timestamping [1]
[2] [3].
There is a student-friendly, hobbyist-grade time stamping board that
grew out of ham radio circles [4]:
This is based on an Arduino with the heavy lifting being done by a
wonderful timing chip originally designed by TI for time-of-flight
measurement. The TAPR TICC does timestamping to better than 100 ps
resolution.
On the other end of the performance spectrum you can do timestamping
using any old laptop and just a serial port. A win32 example is here:
It has its limitations but it shows that a lowly serial port pin can be
used as a trigger for time stamp recording. I use this for quick 'n
dirty low rate Geiger measurements. For more precision and no dead time
I use dedicated hardware for the counting & timing and the PC just for
data logging.