Radar charts, that are similar to Rose charts. Each of the data points is arranged equally in terms of angle, whilst the magnitude of each point is shown by the distance from the centre. Thus, data points of a higher magnitude can be seen as they are more distant from the centre.
Suitable for many datasets, but not all. If not, then Rose charts may be more apt.
The circle, as can be seen in the second example, could be used to indicate a threshold of sorts. In the example, it could be minimum sales required for a particular month. Months that fall below this threshold can be clearly seen.