Quite a lot, actually.
For absolutely no cost to you whatsoever, you can use their website that they paid for and worked hard on to set up and pay for the servers to serve you, to create up to six characters using material from the SRD, Basic Rules, Elemental Evil Player's Guide and your own homebrew which will eventually allow for races, class and feat creation, and you can also have people join a campaign and run it using those resources with the campaign tools which will be expanded upon by launch and after launch, and as an easy to use, searchable reference with hover-over access to the SRD, Basic Rules and EEPG spells, monsters, conditions, etc.