From IFWiki

Trellis is an interactive fiction authoring system for RISC OS computers written by Vince Hudd of Soft Rock Software.

Trellis provides a simple framework into which the key components of the game are added. User editable files define objects, rooms, words and other game text. The main code for the adventure game is written in a BASIC like language customised for interactive fiction authoring; this is interpreted by the Trellis framework.

Trellis is written in BBC BASIC and is supplied with full source code and two example games.