Recently I read asm.js spec and it seems cool but is there any environment/tool to develop and test this tool or not? Is that still on spec phase only?
You can try it by using emscripten with ASM_JS=1 and running it in a firefox build from a side branch. Links and more instructions are in these slides about asm.js, http://kripken.github.com/mloc_emscripten_talk/#/