Main downloads:

Download Glass 2.0 distribution package
Download Opening book manager 1.0
Special version - 64-bit compile for tweaking

Opening books:

Medium (96.000+ positions)
Large (193.000+ positions, under construction, last update 27.11.2011)

Some of the older versions:

Download Glass 1.9
Download Glass 1.8
Download Glass 1.7
Download Glass 1.6
Download Glass 1.5
Glass 1.4 was never released (two independent failures by both developers)
Download Glass 1.3
Download Glass 1.2
Download Glass 1.1
Download Glass 1.0