@Freylet used to recommend habit rpg but I think it's habitica now https://habitica.com/static/home
There are probably better tools for taking fitness specifically but this is good if your goals are reps and "how much have I participated in this task" rather than by weight
@vahnj *Nods lots and lots* Atm we want to learn what we should be doing to lose weight. We will be using something like the Habit RPG once we have learnt the best way to go about losing weight and fitness.