At this time, Ancestry.com does not require a subscription to have a family tree.
To access the tree, a person need to have a login. Their guest login option is free.
I set up a tree in this fashion for a friend who does not have any ancestry subscription.
She can login and edit the tree.
They also have good privacy settings. But, if you use those, people will need an explicit invitation from you to access the tree.
They do require a subscription for data search.