Compared with deriving, Fan is mainly different in such aspects:

1. It generate code without touching your source tree, module is 

the basic unit. We generated code for all modules in ocaml's compiler

parsing/, typing/, and bootstrapped camlp4 source tree itself.

Check here http://www.seas.upenn.edu/~hongboz/hongbo_zhang_files/fan_doc/

All modules beginning with Fan_ocaml is generated code for ocaml compiler

Fan_camlp4ast_o is for camlp4ast itself.

2. composable.  All extended syntax are in our mini dsl language "fan" without polluting the original syntax

3. Lightweight   Check the modules gen_plugins  we write generic printing, equality, map, fold traversal, etc, 9 generic plugins in less than 200 lines of code.

It's still at alpha stage, and I have some ideas that need to be polished, I would be happy to hear any feedback. We hope that FAN can benefit ocaml community as a camlp4 platform. Fan's code base is pretty small, all the Ast Transformations are based on quasi-quotations. The only exception is TyDcl which has no counter-part and Ast Lifting, since the current camlp4 does not support  macro syntax in common lisp something like ``(,,).