GOG introduces a program like "Early-Access" on Steam. They call it "Games in Development".

Published games in this program are still in development, and you have a full 14-day refund guarantee.

The first five games published are:

- Starbound (-33%) (Version for Linux available)
- Ashes of the Singularity (-25%)
- Project Zomboid (-40%) (Version for Linux available)
- TerraTech (-30%)
- The Curious Expedition (-15%) (Version for Linux available)

The english FAQ at GOG answers more questions.

Original-Text:

Excellent hand-picked games, 14-day refund policy, always DRM-free.
We want GOG.com to be the home of games that are both excellent and really worth your time.
In today's gaming world, we're seeing more and more titles that become hits before development dwindles down, we want to give you a way to enjoy what these games have to offer, a way that's comfortable and fair to you — the GOG.com way: that means evaluating each and every game, a 14-day no-questions-asked refund policy, and more.
That's why today, we're introducing the first five games in development:
Starbound (-33%)
Ashes of the Singularity (-25%)
Project Zomboid (-40%)
TerraTech (-30%)
The Curious Expedition (-15%)

Source: GOG