Valve continues to promote the culture of demos. You can explore many projects before release.
The October Steam Next Fest (or "Games to Be") demo festival recently started on Steam. Developers have presented trial versions of projects.
The "Games to Be" festival will run on Steam until October 20th, the promo page is available at the following link: it shows various demos and has a genre filter.
Valve released a trailer for the event, which included a selection of shots from some of the participating games, including: Mad King Redemption, Homura Hime, Warhammer 40,000 Mechanicus 2, Heroes of Might and Magic Olden Era, REANIMAL, PowerWash Simulator 2 and more.
