Fluids have been added to the latest version in my personal repository.

It fixes the withdrawn SRFI 15 by requiring an explicit

(define-fluid <fluid> <expression>)

or

(define-thread-fluid <fluid> <expression>)

to bind a fluid.

The latter version differs from the former only concerning assignment
in the presence of more than one thread;

fluid-let

always behaves well in multi-threaded environments.

Marc