The demo was available for a limited time on GOG.com
For the users that got the demo, it is still available in their Library.
https://web.archive.org/web/20160401150843/https://www.gog.com/game/shadwen
https://www.gog.com/news/play_shadwen_demo_win_prizes

Links for downloading the demo / technical preview.
https://steamcommunity.com/app/425210
https://www.humblebundle.com/store/shadwen

Some technical support for linux users
http://frozenbyte.com/board/viewtopic.php?f=32&t=27507&sid=9d877d84a12fdb7d9c80f15d380158bc
http://frozenbyte.com/board/viewtopic.php?f=32&t=27564