There are a lot of things happening in winter each year, at different times during winter. So this is a Hannukah, Christmas, Kwanzaa, New Year and what have you discount all in one, up until the beginning of January.
You get a nice discount for Urth both on the Android Market as well as Desura.
And
You get another nice discount for the Circularity synths on the Android market.
Links:
Urth on Desura (Linux, Windows, Mac)