Business Card Brainfuck is a tiny Brainfuck interpreter which fits on business cards and is only 512 bytes of code. It's inspired by Business Card Raytracer by Paul Heckbert (more).
It exists mostly to demonstrate how easy it is to implement a Brainfuck interpreter and because I was bored one evening. Indented code is located in bf_indent.c.
#include<stdio.h> // Krzysztof Gabis 2015
#include<stdlib.h> // Usage: ./bf program
int p[64*1024],d[1024*1024],r,c,t,e;int main(int c,char*v[]){
if(c<2)exit(1);FILE*f=fopen(v[1],"r");while(f&&(c=getc(f))!=
EOF)p[r++]=c;r=0;while((c=p[r])){e=0;if(c=='>')t++;if(c=='<')
t--;if(c=='+')d[t]++;if(c=='-')d[t]--;if(c=='.')putc(d[t],
stdout);if(c==',')d[t]=getc(stdin);while(c=='['&&!d[t]){if(
p[r]=='[')e++;if(p[r]==']'&&e--==1)break;r++;}while(c==']'&&
d[t]){if(p[r]==']')e++;if(p[r]=='['&&e--==1)break;r--;}r++;}}
make
./bf filename
./bf hw.bf
curl -s "http://www.99-bottles-of-beer.net/download/1718" > bottles.bf
./bf bottles.bf
curl -s "http://esoteric.sange.fi/brainfuck/utils/mandelbrot/mandelbrot.b" > mandelbrot.bf
./bf mandelbrot.bf