Courtesy of Phoenix Pick you can download Limits, a collection of short stories by Larry Niven, for free. You need to use the coupon 9991295 (you can subscribe to the newsletter to get future promotions, including free ebooks coupons, in your email). This is the description of the book:
Here is an extraordinary mix of fantasy and science fiction from one of the masters of science fiction, Larry Niven.
The stories in this collection include some collaborations with authors such as Jerry Pournelle (Spirals) and Steven Barnes (The Locusts), as well as stories written by Niven himself.
Larry Niven’s credits include the award-winning Ringworld series, his “Known Space” novels and the Man-Kzin anthologies. His collaborations with Jerry Pournelle include such titles as Lucifer’s Hammer, Inferno and The Mote in God’s Eye.