See object-oriented-programming before the remainder of this page.
There are several common libraries for Scheme & particular Scheme implementations that claim to be 'object systems,' for varying definitions of 'object system.'
I already began that by describing more precisely what each of those 'object systems' comprised. E.g., Tiny-CLOS is a hierarchical class-based, MOPful, generic type dispatch system, based on CLOS. It would be helpful if people who added to the list would follow suit, rather than, for example, writing 'Oaklisp's object system.' I'd elaborate on that myself but I don't know much about Oaklisp.
I categorized those a bit. It would still be helpful to have a better description for each. From what I've seen from Oaklisp sources - that's not much - the object system seems to be quite CLOSy (make, add-method), but it might be something completely different...
it is more of a mixture between smalltalk and scheme, no multiple dispatch for example.
It would be nice to have actual code-examples here, so the reader can get a feel for the systems before investigating in detail.
edit-hint I think that we should try to merge this list with the Jonathan Rees object-oriented-taxonomy. Just my thought.