In recent years several new classes of fibers have emerged based on the same basic technological platform - air/silica microstructures. Though they are often referred to collectively these fibers can be divided into three very different classes: air-clad core fibers, effective-index fibers and photonic band-gap fibers. Although all act as waveguides, these groups of fibers exhibit different optical properties leading to different applications. We briefly discuss the air-clad core and effective index fibers before concentrating on the more unusual photonic band-gap fiber. With losses as low as 2.6 dB/km for effective index photonic crystal fibers (PCF) and 1 dB/m for band-gap fibers, this technology is beginning to show its potential for becoming a platform for more than just unique fiber-based components.