While I understand the appeal, "relaxing" games have never been my goblet of dead plant water. What does interest me are those that utilise neat algorithms or systems, like the in-development Starboretum, the work of Eufloria's Alex May. Starboretum right now is represented only in tech demo form, with gorgeous, multi-coloured trees sprouting from the ground and growing increasingly more complex the longer you watch.
Whether Starboretum will become evolve beyond its pure simulation roots into something more game-like remains to be seen — the official site is beyond plain, with a few progress shots featured on its blog.
The game's Twitter account is only a little less vague, describing the title as a "monouser cultivation and transcendence simulator". I wish I could tell you what that means, but it does sound calming.