Charts.module
A drupal module with API that supports High Charts and Google Charts libraries. Views integration
project/
code: https://www.drupal.org/project/charts
docs: https://www.drupal.org/node/2423033 + https://www.drupal.org/node/233753
examples:
Google Charts
docs: https://developers.google.com/chart/interactive/docs/index
examples: https://developers.google.com/chart/interactive/docs/gallery
Charts.js
6 chart types
nice animations; very tin js, leverages HTML5 canvas + cross platform fallback
project: http://www.chartjs.org
code: https://github.com/nnnick/Chart.js
docs: http://www.chartjs.org/docs/
examples:
D3
good for inventing things
...