Right out of the gate, Renderdoc isn't as useful to Linux users as is Valve's VOGL or other utilities like APITrace. Because, as it stands right now, Renderdoc only targets the Microsoft Direct3D 10/11 graphics API, but support for OpenGL is planned under this open-source Renderdoc. While still targeting D3D11 right now, there is basic build support for Linux of Renderdoc. I imagine in the months ahead it will get much more interesting once there's OpenGL API support and open-source contributors have had their hand at improving the Renderdoc Linux support.
Renderdoc had been free to use by game developers since February, but now all of its code is out there under the MIT license and hosted on GitHub.
Crytek says, "By open sourcing development of the debugger, Crytek hope the community will get even more involved in this process and make changes and improvements directly." You can learn more about Crytek's Renderdoc at CryEngine.com.