Frequency 2005.2 is a hardware and software project which enables a PC to measure frequencies of over 20MHz. Simple and effective, a handy tool for the engineer.

PC Frequency meter. 2005.2
This project is a frequency meter that consists of hardware that plugs into your PC soundcard, and software that provides the analysis and user interface.

Version 2005.2 fixes a small display bug and increases accuracy on short sample times.

Link: http://www.opend.co.za/hardware/freqmeter1/index.htm