Want to play a rogue who casts a few spells? A barbarian who does not rage but who can move through the forest like a druid? The variant class system allows these and many other class alterations. Mix and match normal class abilities or add some of the new class abilities contain herein. 29 sample variants are explored in this section.
And that's just the first section of the book. Later section include ways to spend skill points on class features, feats for all occasions including some very high level fighter feats (requiring BAB +16 or greater). There is a section on building prestige classes and a few samples therein.
Next is the monsters as classes section that was previewed way back in January. This section contains a method for playing any monster that advances by character class from level 1. Even drow, hill giants and lycanthropes. The final section contains templates for adding special attacks and special qualities to critters or characters that don't have them. Want a race of elves with poisoned stinger tails? Or a race of dwarves with ram's horns? They are in there. Want to add fire breathing to character? You can.
All that and it's 100% OGC. Enjoy.