Recently Isaac proposed that using non-free, i.e. pay-to-use, languages for cops and robbers challenges should be considered a standard loophole. As Dennis stated in a comment, there is some ambiguity in this. Namely, what constitutes "free enough" to be able to use?
Some languages have free trials, though once the trial period expires, the language is no longer available for use. Examples include Mathematica, Matlab, Stata, and LabVIEW.
Some languages are free to use but are only available for particular operating systems. Examples include AppleScript and Windows Batch.
TI-BASIC can be emulated, but it's illegal to do so unless you own a Texas Instruments TI-84+ calculator.
What should our standard be for allowing such languages for cops and robbers challenges? That is, where do we draw the line for "free"? Note that the goal here isn't to obtain a strict set of rules that will be applied blindly to all languages, but we should at least establish a few ground rules.
Please post one suggestion per answer so the community may vote on them individually.