Wikipedia should give an overview but it is also biased toward article authors. The current article https://en.wikipedia.org/wiki/Knowledge_Organization_Systems is very brief and the article on https://en.wikipedia.org/wiki/Conceptual_system is mixed with articles about KOS in some languages. See https://www.wikidata.org/wiki/Q6423319 and https://www.wikidata.org/wiki/Q3622126 in Wikidata.