bsdsar is a simple set of programs to log the usage of a FreeBSD based system over time.  It is very useful if you have a server that is used for NFS, web, ftp, samba, etc, serving and you need to know how heavily loaded the box is.  

Command line arguments:
Options:
 -n day#
 -f file
 -v version info
 -a show all recorded data
 -u cpu
 -d disk
 -r memory & swap
 -i net
 -I net / second
 -N nfs
 -s show top 5 cpu heavy processes
 -S show top 5 mem heavy processes

No arguments results in the current days cpu usage:
bash-2.04$ bsdsar   
Time     % User  % Sys  % Nice  % Intrpt  % Idle  
00:00       0      0       0        21      79
01:00       0      0       0        20      80
02:00       0      6       0        18      76
03:00       0      1       0        20      79
04:00       0      0       0        20      80
05:00       0      0       0        19      81
06:00       0      0       0        20      80
07:00       0      0       0        22      78
08:00       0      0       0        20      80
08:20       0      0       0        21      79


With the -n function, you can see data from any day:
bash-2.04$ bsdsar -n 05 -u
Time     % User  % Sys  % Nice  % Intrpt  % Idle  
00:00       1      0       0        20      79
01:01       0      0       0        20      80
02:01       0      0       0        21      79
03:01       0      0       0        20      80
04:01       0      0       0        21      79
05:01       0      0       0        20      80
06:01       0      0       0        20      80
07:01       0      0       0        19      81
08:01       0      0       0        20      80
...

Notice that you need an argument with the -n function.

You can specify many arguments on one line:
 bsdsar -u -d -f /var/log/bsdsar.dat -n 12
 bsdsar -i -n 0301
 bsdsar -r

Or a:
 bsdsar -a
shows all recorded data for that day.