Simple command that takes lines as input and output the number of lines received during one second. Example:
$ yes | freq
1031638 lines/sec
1031801 lines/sec
1031613 lines/sec
The main problem I was trying to solve, and I wanted the information fast, was to determine how many requests per second my webserver was handling. It was something like this:
$ tail -f /var/log/foo.log | freq
945 lines/sec
862 lines/sec
902 lines/sec
If you happen to find another cool use for this, just let me know :)