Hmmm, after reading the simple explanation PDF of Fractal Trees, they sound more like Dancing Trees than I'd assumed, but I am a poorly informed outsider. The key feature, from a performance perspective, is that writes are minimized by making each write do more, though both also help with SSD wear as a side effect. So, from the outside, it looks like both accomplish many of the same goals, and they do it by fundamentally altering B-tree implementation with modern hardware in mind.

But, this isn't my area. I only have a passing understanding of Dancing Trees (my previous business led me to following ReiserFS closely, but I haven't paid any attention to filesystem or database performance in 7+ years), and no real understanding of Fractal Trees. I'm glad it's Open Source, however, and thanks for the pointers.