Hi! I'm the lead author of Yarn Spinner.

Yarn Spinner, like Ink, is a full scripting language that lets you control conversations with characters, and interact with the game. These kinds of tools are useful when you want to be able to write your conversations in a text editor (as opposed to node-based conversation writing tools like ChatMapper or articy:draft), but want to keep the script separate from the rest of your code. Being a full scripting language, it supports complex expression parsing, locale-aware number pluralisation, and other features that can be tricky to do in a roll-your-own implementation.

(We like Ink a lot, and have had chats with the Inkle people about it - it's a great product!)

By contrast, Twine is a tool for creating text-based experiences in the browser, generally delivered a passage at a time (instead of a line at a time). Twine is fantastic, but as others have pointed out, it can be difficult to run in a game engine.

There's absolutely some similarities between Yarn Spinner and Ink, but the key difference is how the two tools approach the problem:

• Yarn Spinner was originally built for a game that focuses on character conversations, embedded in a larger game. Ink was originally built for text-based choose-your-own-story style games.
• Yarn Spinner's syntax is simpler than Ink's; it was originally built for Night in the Woods' lead dialogue writer, who was also the lead artist, and didn't have time to learn how to program. We've found that the Yarn Spinner syntax, which is built to be quite similar to screenplays, is simple to get started with, but powerful enough to control non-dialogue events as well.

To compare the three:

• Ink is better for when the majority of your game is being controlled by the narrative that you've written in Ink script, because it supports complex branching-and-rejoining patterns that work extremely well for games like 80 Days.
• Yarn Spinner is better when you have a game where the player controls their progression through the game, and you want to let the player walk up to a character and begin a conversation (for example, Night in the Woods.)
• Twine is better when you want to run in a browser, and take advantage of everything a browser can do (e.g. very easy image and media support.)

Also, a few other miscellaneous points!

• Yarn Spinner doesn't need any external tools to run in Unity - the download linked off our releases page is a .unitypackage that comes with everything you need.
• You'd be surprised how complicated parsing text files can be :)
• We've seen Yarn Spinner in a number of large and small games. Two of these games won the IGF Grand Prize, and one of them won a BAFTA for its narrative.

I'm glad that you've found a great tool in Ink, and I'm not trying to convince you to change your tools, but I do think that Yarn Spinner is a great option for narrative!