beef is a BrainFuck interpreter, that is, a program which executes BrainFuck code on the fly.
Its behavior is configurable using command-line options, so you can run most BrainFuck programs written for many other interpreters/compilers without modifications.
beef gets rid of some historical BrainFuck limitations: for example, the length of the memory tape has no limits except for the amount of memory your computer has.
beef's aim is not to be incredibly small or optimized, but to be a flexible and pleasant-to-work-with interpreter.