use the HLSDK without Valve's HL engine is illegal as it has strict non-free license. You also have to write all MOD codes yourself.
Valve's main purpose to release the HLSDK seems to be get some people working for Value for free (just think about the early age of CS), rather than serving the hobbies or contributing to the community.
edit: this one seems can render HL maps:
http://fteqw.sourceforge.net/