Cube is an open-source system for visualizing time series data, built on MongoDB, Node and D3. If you send Cube timestamped events (with optional structured data), you can easily build realtime visualizations of aggregate metrics for internal dashboards. For example, you might use Cube to monitor traffic to your website, counting the number of requests in 5-minute intervals.

Cube supports filters for aggregating a subset of events: you might filter requests for a specific path, host, or user-agent. Or perhaps plot the count of slow requests (>500ms) over time. You can also evaluate arithmetic expressions, even combining multiple event types, say to compare requests to signups for conversion tracking.

Requirements: Javascript Framework
Demo: http://square.github.com/cube/
License: Apache License