A success community member needed to create a simple tabular report showing just one open task per opportunity. This can be achieved by Rollup Helper. Such a solution allows for key details from the open task to be displayed at the opportunity, so that no custom report types need to be created or so that a simple opportunity list can be created for each sales rep that shows them their follow-up list of opportunity-related tasks. I thought this was a really cool idea and more details on which fields to rollup are included in this post: