Re: Docker tweaked its terms of service
Two different issues.
There can be no contract if there is no consideration. That's simply an essential element of a contract. One might argue that supplying of containers for the service to share represents consideration - but that is a separate and complicated question (I think we get into discussions about weighing boilers at that point)
In terms of unilateral changes - assuming a contract exists - if you agreed in the original TOS to unilateral changes then you can't really complain and its perfectly legitimate (mostly - there are some limits to that in most jurisdictions) - if you didn't then they can't be changed.