- YUI (Yahoo User Inferface) offers open source charts, widgets, and other tools, many of which drive Flickr and Yahoo Mail.
- Mashi offers tools for making sprites and letters dance across the screen.
- MooTools offers browser-independent shorthand for manipulating arrays, divs, spans, etc.
- Pp3Dico helps create 3D game boards.
- VideoForEverybody lets you use standard HTML5 tags that will be replaced with Flash or QuickTime if the viewer's browser doesn't support HTML5.
- Raphaël simplifies work with vector graphics.
- JSCharts provides chart templates.
- Flot plots data on a graph.
- Protovis provides data visualizations.
- Simile Widgets offers another collection of data visualization tools.
- Tile5 offers interesting mapping capabilities.
- jQuery Mobile makes it easier to create touch-friendly mobile apps.
- HTML5SQL makes it easier to take advantage of local databases.
- TaffyDB accomplishes querying tasks with JSON.
- Firebug provides debugging capabilities.