D20 Modern Roleplaying Game by Bill Slavicsek, Charles Ryan, Jeff Grubb, Rich Redman (2002, Hardcover)

Though I am not especially fond of the modern incarnation of D&D (certain thematic and design flaws continue to haunt this game even after 30 years), I found myself pleasantly surprised with D20 modern. Although its mechanics are virtually the same as those used in D&D (Editions 3.0 and 3.5, anyway...I've yet to experience 4.0 for myself), D20 Modern makes better use of the character class concept than any of its predecessors. In D20 Modern, flexibility is the key: multi-classing and customization are easy as you please, allowing players to create the type of characters they actually want to play, as opposed to being forced to "settle" on a character class that doesn't necessarily capture what the player was hoping to create. D20 Modern also proceeds from the very outset with the idea that the rules must work in multiple campaign settings, some with vastly differing design theories, and the book even includes a few abbreviated campaign settings to illustrate this flexibility. In addition, all the bells and whistles of fantasty and sci-fi gaming are touched upon herein: magic, psionics, firepower, high-tech gadgets...what a terrific toybox!

The organization of the core rulebook is a trifle bewildering at times, but D20 Modern is a terrific gaming engine with a solid design stance. You'll probably want to pick up the Menace Manual supplement to populate your game with well-balanced foes, but for the most part, the D20 Modern book is surprisingly complete and highly functional.