During my thesis and postdoc years I have produced several implementations of cosmological models in different codes:
You can also visit my Github page to see what I have made public or email me if you are interested in codes not released yet.
Some codes that I like:
My codes of choice to obtain predictions for models representing fundamental physics are CLASS and CMBEasy (the latter one becoming less useful, as it is not maintained). Although I use it less, I find the CAMB online tool very useful.
There are two excelent packages for Mathematica that I strongly recommend:
xAct is able to handle symbolic computations within differential geometry in a very general way, but it is difficult to learn. RGTC is very easy to learn, but limited to tensor computations in a given set of coordinates.
Code Monkey by Jonathan Coulton