How many developers?

[Joseph Koshy]

If you'd like approximate activity levels by committer, 
try something like:

% cd /cvs/FreeBSD/CVSROOT-src/commitlogs # choose repository
% gzip -dcfq * | awk '
  /^[a-z][a-z]*/ { count[$1]++ } \
  END { for (c in count) { print count[c], c } } ' | \
  sort -nr | less

... 
7193 jkh
6864 peter
6682 phk
6031 obrien
5898 ru
5261 bde
4355 ache
3737 imp
2951 brian
2867 jhb
2765 des
2399 rwatson
... [snip] ...

For 'recent' activity levels, replace the '*' with a suitable
set of commit logs.

I'd also like to point out that most of the changes to the
project come from outside of the group of 'committers' (I
remember a figure of 75% doing the rounds at one point).  
The number of  FreeBSD 'contributors' exceeds the number 
of committers by a large margin.

--
FreeBSD Volunteer, http://people.freebsd.org/~jkoshy