every is a simple tool, that shows every n'th line (hence the name) or up to m lines every (n-1)'th line of its stdin.
It can be used as a poor-man's status monitor for output intense programs.
Simply compile it using ghc.
ghc -O2 every.hs
every [n] [m]
jot 10 | every 3
produces
3
6
9
and
jot 10 | every 4 3
produces
4
5
6
10