GtkDatabox is a widget for live display of large amounts of fluctuating numerical data. Data presentation (e.g. on linear or logarithmic scales, as dots or lines, with markers/labels) as well as user interaction (e.g. measuring distances) is easy.
While it's very useful as a starting point, it has a long way to go in terms of documentation and could benefit from greater flexibility of layout. Also, there are a few bugs.