From the Index Chaotica series from the Black Library comes the Eye of Terror digital release. I have been very interested in this series, but have yet taken the plunge to check them out. This however may end up being my first of the small miscellaneous digital releases.
via the Black Library
The Eye of Terror is a giant Warp rift into which the Traitor Legions fled after the Horus Heresy. Time flows differently within the Eye of Terror, and there are many Daemonic worlds inside. Pouring forth from this rift come numerous Chaos incursions to plague the Imperium.