I remember what heero was saying about microprogramming, so I thought this was worth posting. Its an IP stack (sort of) that fits inside a Twitter tweet.
http://www.sics.se/~adam/twip.html
Code:
char b[140];unsigned short *s=b;*l=b;t;main(){while(1){read(0,b,140);b[20]=0;s[11]+=8;t=l[4];l[4]=l[3];l[3]=t;write(1,b,140);}}