There aren’t too many free options for charting on the web, either client-side or server-side, that provide you with the actual charting code. We recently reviewed Google Charts, a web-based API for charting from Google. However, either for internal controls, or just simplicity of implementation, sometimes you need to do your own charting with a free software solution. Here are some of the better options, both purely JavaScript/Flash, as well as those with server-side bindings.
Flot
Flot is entirely client-side, powered by jQuery and using HTML <canvas> (or the excanvas library for emulating IE support). The demos provided are quite comprehensive, and the API is simple yet powerful. Being pure-Javascript, it’s also fully portable to projects where server-side scripting is unavailable (e.g. Adobe AIR). Flot-drawn charts are attractive out of the box, although everything can be configured. Zooming functionality is also included.
Open Flash Chart
Open Flash Chart, a Flash-based chart system (no surprises here), features a very powerful API, possibly more so than most other options (including commercial offerings!). It has an interesting approach to chart generation – it fetches chart data from the server; the object makes a seperate HTTP request to fetch the dataset.
Plotkit
Plotkit is another JavaScript-based charting solution using <canvas>. It also supports SVG thanks to Adobe SVG (given browser support, of course) – SVG graphs scale beautifully with Firefox 3′s image-resizing on the fly for client-side zooming. It uses Mochikit 1.3+, and excanvas for IE6 support.
Flotr
Flotr, inspired by Flot (see above), is a simple JavaScript charting library built on Prototype. Flotr focuses on drawing appealing graphs with simple syntax; the snippets for its examples are generally a little leaner than those of the other JS libraries. Flotr comes with fairly thorough documentation available online, to help you get up and running quickly.
Honorable mention: PHP/SWF charts
PHP/SWF charts isn’t entirely open source, but I’ve included it with an honourable mention given its popularity. It offers a free version, with almost all the features of the commercial offering ($45/domain). With PHP bindings, it’s possibly the easiest to get started with if you already use PHP in your application, and its sister project XML/SWF charts happily takes any other server-side language. It also has the most visually appealing demo charts.
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