Brainfuck

bf.js

with(process)for(a=[k=j=p=0],l=[];c=argv[2][k];k++){c=='['&&l.unshift(a[p]&&l[0]!=-1?k:-1)
c==']'&&(a[p]&&l[0]>=0?k=l[0]:l.splice(0,1))
if(l[0]!=-1){p+=c=='>'?1:c=='<'&&-1
s=c=='+'?1:c=='-'&&-1
a[p]=a[p]==undefined?s:a[p]+s
c=='.'&&stdout.write(String.fromCharCode(a[p]))
c==','&&(a[p]=argv[3].charCodeAt(j++))}}

Here's a more readable version: https://gist.github.com/4eecbc79053032a5d9eb

Save this as bf.js and run with:
node bf.js "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>."

Simple cat program:
node bf.js ",[.,]" "Hello World!"