As of now, three ebooks by John Ringo can be downloaded for free from Amazon (in addition to Gust Front, which is still free). The books are the following:
WITH FRIENDS LIKE THESE . . .
With the Earth in the path of the rapacious Posleen, the peaceful and friendly races of the Galactic Federation offer their resources to help the backward Terrans—for a price.
Humanity now has three worlds to defend.
As Earth's armies rush into battle and special operations units scout alien worlds, the humans begin to learn a valuable lesson: You can protect yourself from your enemies, but may the Lord save you from your allies.
There Will be Dragons (Amazon US, Amazon ES)The Battle Against
to Rule the World—or
In the future the world was a paradise—and then, in a moment, it ended. The council that controlled the Net fell out and went to war, while people who had never known a moment of want or pain were left wondering how to survive.
Duke Edmund Talbot has been assigned a simple mission: Go to the Southern Isles and make contact with the scattered mer-folk—those who, before the worldwide collapse of technology, had altered their bodies in the shape of mythical sea-dwelling creatures. He must convince them to side with the Freedom Coalition in the battles against the fascist dictators of New Destiny. Just a simple diplomatic mission. That requires the service of a dragon-carrier and Lieutenant Herzer Herrick, the most blooded of the Blood Lords—because New Destiny has plans of its own.
The fast-paced sequel to There Will be Dragons is a rollicking adventure above and below the high seas with dragons, orcas, beautiful mermaids— and the irrepressible Bast the Wood Elf, a cross between Legolas and Mae West.
In the future there is no want, no war, no disease nor ill-timed death. The world is a paradise—and then, in a moment, it ends. The council that controls the Net falls out and goes to war. Everywhere people who have never known a moment of want or pain are left wondering how to survive.
But scattered across the face of the earth are communities which have returned to the natural life of soil and small farm. In the village of Raven's Mill, Edmund Talbot, master smith and unassuming historian, finds that all the problems of the world are falling in his lap. Refugees are flooding in, bandits are roaming the woods, and his former lover and his only daughter struggle through the Fallen landscape. Enemies, new and old, gather like jackals around a wounded lion.
But what the jackals do not know is that while old he may be, this lion is far from death. And hidden in the past is a mystery that has waited until this time to be revealed. You cross Edmund Talbot at your peril, for a smith is not all he once was. . . .