A demo for Serious Sam: Double D is now available on Steam, according to a press release. The side-scrolling shoot 'em up was released earlier this year.
The demo features two of the eighteen campaign levels and two of the twelve challenge rooms. The demo can be picked up from Steam here.
Serious Sam: Double D is the first title in the Serious Sam Indie Series, which is available for the budget price of $7.99 USD.