Vaesen - Nordic Horror Roleplaying Core Rulebook - Rules of Play says:
Vaesen – Nordic Horror Roleplaying is written by Nils Hintze and based on the work of Swedish illustrator and author Johan Egerkrans. Vaesen presents a dark Gothic setting steeped in Nordic folklore and the old myths of Scandinavia. The game mechanics utilize an adapted version of the awardwinning Year Zero Engine.