In a Table, Line chart, Area chart, Column chart and Pie chart widgets you are able to group by a 'Custom field'.
Choose 'Custom field' as 'Group by' in the settings box on your widget.
Select your data source and field you want to group by in the new line that appears.
In the below example I have grouped by shops to see who sells most - but you can group by customers, stages, status etc.
This GIF shows a group by stage from Pipedrive (open deals). This will give you an overview of how many open deals you have per stage all time.
Please be aware of the following:
Because of performance reasons, the maximum number of groups that charts will display is now 100 (these are lines, pie slices and columns). Anything close to half that number is anyway un-readable:
Therefore, you might consider displaying this in a table, which can show up to 50 lines.