This image comes from recently released tech demo of nGENE Tech engine - open-source 3D engine. It can be downloaded here. More info on nGENE Tech can be found on its homepage.
There is also rich screenshots gallery available here.
You can also watch movie presenting several nGENE effects here.
Submitted screenshot presents following techniques:
* Preetham daylight model with added sun glare
* Terrain rendering
* Clouds with light scattering and fade out towards horizon
* HDR (I know it's impossible to tell it from the picture)
* Water rendered as a post-process effect - only tuning has be done since last submission but it looks a lot better now. There is translated presentation from my lecture during IGK'2009 conference which is available here. The water is rendered in screen space and I focused on modelling proper light extinction.
The demo itself features a lot more but it is impossible to present everything in one picture:
* animated vegetation
* animated water waves propagation
* a lot of effects to apply (eg. SSAO, water colour effect, Black & White filter, sepia filter)