I recently wanted to show (demo) an app I built to another client but obviously couldn't use original client data. I wanted to showcase the export, filtering and dashboard (graphs, pivots tec) and need a lot of data to do this.
I came across this super little tool for creating dummy data.
Just download the data from an existing Knack object (table) and using the the CSV file you download delete all content but keep header rows. You can then use this empty CSV to create the table headers for your schema in this mockroo tool. You then create rules around the type of data you want. You can save the whole schema and refresh with more dummy data when ever. Its free up to a point also