An addendum to the "progress" section....
SpaceX has been flying cargo to the International Space System for some time using their Dragon capsule. A few days ago they completed their first manned mission on the Crew Dragon.
Three big items from this:
1. They have a reusable cargo/crew capsule for LEO operations.
2. They have gained experience in building human life support systems and associated ground operations.
3. They implemented autonomous docking for both the cargo and crew variants of Dragon. This is one of the keys to achieving in-orbit propellent transfer. Item (2) in my original post.