This is a small web app to visualise the Darboux sums for different functions.
Currently you can choose from 6 functions, and you can set the domain to be any closed interval. You can also choose the number of sub-intervals in the partition - but note that at the moment the sub-intervals are always the same width. In general the sub-intervals can be different widths - I may implement this at some point in the future.
A live demo is available here
See the Wikipedia page for more information about Darboux sums.