A couple of ideas for typography animations and letter (hover) effects for playful interactions. Anime.js is used to create animations.
span injector for radical Web Typography.
A tutorial about creating set of inspirational letter animations for display typography effects and large headlines powered by anime.js
Type.js adds new type properties to your CSS, giving you the control you need for type on the web. You can write these properties in your CSS and they will work like any other property.
Blast.js separates text in order to facilitate typographic manipulation. It has four delimiters built in: character, word, sentence, and element. Alternatively, Blast can match custom regular expressions and phrases.
Blast's uses include typographic animation, juxtaposition, styling, search, and analysis.
FlowType.JS is a plugin for Responsive Web Typography at its finest: font-size and line-height based on element width.
FlowType.JS is changing the font-size—and subsequently the line-height based on a specific element's width. This allows for a perfect character count per line at any screen width.