dygraphs is a fast, flexible open source JavaScript charting library.

It allows users to explore and interpret dense data sets.

The chart is interactive:

• you can mouse over to highlight individual values.
• You can click and drag to zoom.
• Double-clicking will zoom you back out.
• Shift-drag will pan.
• You can change the number and hit enter to adjust the averaging period.

Features:

• Handles huge data sets: dygraphs plots millions of points without getting bogged down.
• Interactive out of the box: zoom, pan and mouseover are on by default.
• Strong support for error bars / confidence intervals.
• Highly customizable: using options and custom callbacks, you can make dygraphs do almost anything.
• dygraphs is works in all recent browsers. You can even pinch to zoom on mobile/tablet devices!
• There's an active community developing and supporting dygraphs.