An associate of mine on Twitter by the name of Trevor Williams https://twitter.com/tw_trevorwrites will be publishing his upcoming Sci-Fi novel very soon (name will be announced soon). He will be hosting a contest in which he will be giving away some free copies along with other goodies. I had the privilege of reading an early copy and it's a fantastic nail-biter. Trevor is a very talented author.
I'd tersely describe it as "The Martian" meets "Independence Day" meets "Armageddon". Two SETI scientists and a wealthy Aerospace mogul team up to save the world from an incoming alien threat to Earth in an alternate 2014 timeline.
Keep a lookout on his Twitter page for rules and when to play.