I needed to spin up a new wiki recently for a specific purpose and settled on wagn as something that looked interesting -- and, since it's a rails app, something I can hack at if it turns out to be not quite what I want.

The thing that's interesting about wagn, to me, is the conceptual integrity of making everything a card -- I'm not sure that the essential simplicity of that notion is currently expressed in the most accessible way it might be (in terms of becoming proficient as quickly as possible after first being exposed to the system), but that is perhaps a documentation issue rather than a code one.