Indices : Tools : Type Design Tools : Visual OpenType Layout Tool (VOLT)

A GUI tool from Microsoft for managing the complex set of substitutions possible in OpenType fonts. Freely licensed to developers who join the VOLT community web site. Easier to use (according to John Hudson) for some complicated substitution tasks than the Adobe FDK used by FontLab and TypeTool, such as contextual positioning and dealing with feature precedence in complex scripts.

Discussion:
OpenType Tables and VOLT
Visual OpenType Layout Tool (VOLT) version 1.2 posted
Anchors in FontLab?