Screen layout. Late-80s commercial IF and recent commercial and amateur IF all featured an explosion of different screen layout experiments. This Pinterest board covers a number of different user interface experiments in IF, including multimedia resources, while posts I’ve written specifically about interfaces appear here.
Real-time input. Events continue without pauses for turns; the player’s input takes effect when he has managed to type a command and press return. The realtime and real-time tags on IFDB (unfortunately not totally standardized) list several dozen such games as of late 2014. Border Zone is a famous early example from Infocom, but there have been a number of experiments in this area since, both using standard IF systems and using hand-rolled methods.
Multimedia. The use of pictures and sound in IF is increasingly common and increasingly easy to achieve. IFDB lists games that include graphics or sound. For Inform, the GLIMMR extension package provides advanced editing functions and frameworks for automated mapping and more.
Map navigation. Some pieces provide built-in maps of the game space for the player’s convenience, which are either visible in full at the start of the game or fill themselves in gradually as the player progresses. A few choice-based works also explicitly map the plot structure as orientation for the reader.
Parser-driven work. Many games classically considered IF (including a lot of my own) are based on parser input. I’ve written a bit about some of the challenges of the parser, though it also remains a much loved format within the community. Games listed on IFDB, especially those from before 2010 or so, are typically parser-based unless otherwise noted. This article by Carolyn VanEseltine addresses some specific design challenges associated with parser games.
Choice-based work. Choice-based works are those that allow the player to make explicitly enumerated choices. Works written in Twine, inklewriter, StoryNexus, Varytale, ChoiceScript, the Choose Your Story system, and Undum all generally count as choice-based, as do classic Choose Your Own Adventure stories. Choose Your Own Adventure is in fact trademarked, but this doesn’t stop the IF community from habitually referring to work of this type under the umbrella term CYOA.
Parser/choice hybrids. A handful of games experiment with combining the advantages of parser and choice systems in various ways: for instance, by building CYOA with an parser game-style world model.
Narrative chatbots. Chatbots are those that take natural language input and attempt to respond in the voice of the character, often using chatbot programming tools such as AIML or ChatScript. Few games of this type are listed on IFDB as of late 2014; it’s a relatively underexplored area.
Freeform input. Some games feature a large or small portion in which the player is allowed to type anything she likes, either to offer a reflective choice (one that matters to the player’s experience but doesn’t affect the game system) or in order to store that text and show it again subsequently.
Narrative of objects. A handful of interactive stories actually take the form of collections of objects for the reader to explore and piece together. This kind of thing is typically not computer mediated and therefore not often listed in IFDB, but for instance Dennis Wheatley’s crime dossiers would fall into this category, as would the suitcase of things constructed by Rob Sherman for the Black Crown project.
Physical books. CYOA and gamebooks were a starting point for the discipline and are still published now. Nathan Penlington’s blog contains a number of great posts listing and depicting different types of interactive book, and items on this blog in the book category may be physical choice-based volumes.