GLS - Generic Little (Object, Type, Anything, ...) System
It provides multiple dispatch for Racket.
Differences from Swindle:
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Doesn't force you to change all. GLS is a small collection with a dozen of functions in API. It only adds generic functions.
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It based upon types, not classes. You may dispatch you function on any predicate you may imagine:
exact-integer?,(real-in 0 10),(and? stream? (not/c stream-empty?)), ...
GLS is based on Greg Sullivan's GLOS, that was witten for scheme48. It has the same API, but without implemetation of own object system (glos-records). So GLS is not "generic little object system", but simply "generic little system". But I added support for racket/class: you may use class instead of type predicate and GLS correctly supports subtypes (subclasses).
Sorry for bad documentation: for API look into main.rkt, for examples of use -- test.rkt.
Some description of GLOS is in the paper ref-dyn-patterns.
Also, slides in proglangsandsofteng work through some examples using GLOS.