The Game Author's Guide to Glulx Inform, for Inform 6.21(G0.35), by Andrew Plotkin.
The Glulx Inform Technical Reference, for Inform 6.21(G0.35), by Andrew Plotkin.
Gull, a guide to Glulx Inform, by Adam Cadre. This archive contains the guide in HTML format.
Gull, a guide to Glulx Inform, by Adam Cadre. This archive contains the example games discussed in the guide.