For those of you who play Dungeons & Dragons, you may have heard about d20 Modern, which brings the excellent and open d20 rules that govern D&D v3.5 to the realistic present day. Well Wizards recently released a suppliment called d20 Future which allows for adventures in any kind of possible future setting you wish to concoct.
I am almost finished reading the book, and highly recommend picking it up if you're more of a sci-fi RPGer than fantasy.
First you've got to love the d20 System; some of the cooler cyberpunk RPGs like Shadowrun were almost unplayable due to agonizingly slow and poor combat rules.
Second, I really enjoy the tone of the book, it's set up as a fairly comprehensive collection of rules for a variety of time periods and technology levels instead of a self-contained campaign sourcebook. d20 Future leave a lot of balance and other considerations to the GM appropriate to the particular campaign.
Some things aren't perfect such as in the Robotics section, the need for sleep isn't explained to my satisfaction nor is the robotic difficulty with hovering in the age of flying cars and skateboards. More than likely, this is an attempt at balance for Robotic PCs and can certainly be changed where pertinent.