I used to keep a journal and found it very therapeutic writing my innermost thoughts and then as I got older I'd laugh at the things that stressed me out when I was younger. Then my mum found it one day and started reading it and that put an end to it... I've tried doing it online but it's just not the same as writing it in a beautifully bound journal and flicking through the pages.
The fact that they send you an email daily
And in the same email they also put a random memory from your past has really helped me stick with the habit.