I am pretty sure that putty is portable. I think portable here is referring to being able to run software from a USB drive without running an installer or just

I am pretty sure that putty is portable. I think portable here is referring to being able to run software from a USB drive without running an installer or just being able to download a file into a temporary folder and removing trace of it by deleting the folder when done. I feel a lot of the initial love for putty was the fact that it was portable (and it also helped back in the day that the download was so small, too.) It is possible as far as I know that it doesn't meet the formal definition in some way, but since you used the term in air quotes and didn't qualify it (like 'but it stores settings in the registry' or similar), I think you may be interpreting the term differently (i.e. I don't think the term is being used to suggest that you can use the same executable across operating systems.)