Greenlight first came out in 2012 as a democratic gateway that determined which games made the final cut to Steam based on player votes. However, Valve felt there were problems with the system. While Greenlight was great for popularising games like Stardew Valley and 7 Days to Die, and over 63 million of us have played games submitted to Greenlight, lots of great titles were getting lost in the noise and fake positive reviews were being posted.
So as of 6 June, 2017 Greenlight is no longer accepting new submissions and voting has been suspended. Starting 13 June, Steam Direct will be the new path for developers to bring their game to Steam.