distributed development methodology

[Adam Jensen]

If one were to develop a Python application on multiple machines, what
are some good methods for keeping them synchronized? For example, I
develop on a FreeBSD machine and a CentOS machine, each with python2.7
and differing sets of site packages. On each machine, I can use
virtualenv. But if I 'pip install xxx' on one, should I just try to
remember to do the same on the other? I am not sure about the details
but syncing the entire virtualenv directory with a DVCS seems like it
might be problematic. (I prefer https://www.fossil-scm.org).

So what are some of the more successful distributed. multi-platform,
development models?