Is there a python equivalent of Ruby's 'rvm'?
Yes, it is virtualenv along with virtualenvwrapper.
update: you may install both at once with virtualenv burrito.
Update: the correct answer is now probably pyenv.
For scientific computing, the corresponding tool is anaconda.
Pythonbrew is no longer under development. The former maintainer suggests to use "PyEnv" instead (see below)".
pythonbrew has come!http://github.com/utahta/pythonbrew