Wizards of the Coast has release the 4th Edition SRD and Game System License. It’s not as liberal as the 3.5e version. You are required to register the with them and actually own a copy of Dungeon & Dragons 4th Edition if you want to use it.
The Dungeons & Dragons 4th Edition Game System License (D&D 4E GSL) is a license that allows third parties to use certain intellectual property owned by Wizards of the Coast with the company’s permission in order to create products compatible with the 4th Edition of the Dungeons & Dragons Roleplaying Game.
The System Reference Document (SRD) is a reference document detailing Terms, Tables and Templates that are available for license under the GSL. The SRD is an appendix to the GSL.
The Official Website of the Dungeons & Dragons 4th Edition Game System License and System Reference Document.