Ways to specify different versions of nodes? I'm creating a dev portal for a client's software, and they would like to have nodes pertaining to different versions of the software in the documentation. 

Rather than have to make an entire new set of nodes for each version of the software, I would like to be able to add/edit a 'version' of the node that pertains to 1.x 2.x etc, within the node edit screen, and control what version the end user sees with a custom module and/or $_GET variable.

My first thought is to use the translation module since this is essentially the same thing, albeit with languages instead of software versions, but I was wondering if anyone had any ideas of what method I should go about doing this?
In this case, go with taxonomy terms. That way you can organize content around a taxonomy term, one for each version. You can even tag content that is applicable to multiple versions just by selecting taxonomy terms.

Then, you could create a view that says "give me all of the content related to version X" and you'd be able to see those. Plus if you ever wanted to do more than "just nodes" e.g. other entities or bundle types, you can just add the field to those bundles and go on your merry way. Plus, since taxonomy terms are entities, you can add fields and content to those terms and build pages that surround those terms.