A solo event is a one-off running event in which you have to complete your chosen distance in one run within the time period stated for the event.
A challenge event is an accumulation running event whereby you can run as many times as you want within the time period and all distances get added to your total until you reach your chosen distance. Challenge event rewards will be linked for the duration of the series. The first series is the 'Wonders of the World' from 1 July '19 until 30 June '20.
An open event is can be similar to both solo and challenge events, however you can sign up anytime and complete your chosen distance in as much time as you need as there are no specific dates.
A free event is a practice event in the same style as a solo event, however there is no entry fee. You will also receive a reward for completing your run.