What restrictions are there on a Winstep license??
Is it node-locked to one machine?
Can I use the program on multiple machines, if I'm the only user of those machines?

Well, Dr Winstep chose not to respond to this message, but in case someone comes across this post later, I want to pass along what he told me elsewhere, before I registered:

//***************************************************
winstep
subject: Re: Losing registration ?
Posted: Tue Jun 02, 2015 6:44 am
Site Admin
There is no such document [ a license file ], but you can hear it straight from the horse's mouth:

1. Winstep license keys are NOT hardware locked.
I personally hate that with a passion.

2. You can use the same key on multiple computers provided you are the only
one using them and you don't go overboard with it - otherwise you would be
better off buying the Home Network license (for the price of less than two
licenses you have written consent to use the same key on up to 5 different
computers).