Visual OpenType Layout Tool
The Microsoft Visual OpenType Layout Tool (VOLT) provides an easy-to-use graphical user interface to add OpenType layout tables to fonts with TrueType outlines. It is licensed free and can be downloaded from the online community set up for it.
VOLT supports a wide range of substitution and positioning types. It also contains a proofing tool for reviewing the application of layout table lookups. It allows import and export of glyph names, lookups, glyph groups and a full project.
The tool has been used by community members to add OpenType layout tables to various fonts supporting scripts, including Arabic (Naskh and Nastaliq writing styles), Bengali, Cyrillic, Devanagari, Greek, Gujarati, Gurmukhi, Kannada, Latin, Sinhala, Syriac, Telugu, and Thaana.
VOLT forums and community