A few months ago we created dinamicherosa.com, a fertility calendar targeting the Italian web. Since we started to got users and even if there are already big p

A few months ago we created dinamicherosa.com, a fertility calendar targeting the Italian web. Since we started to got users and even if there are already big players in the international market, we are going to launch this English version of the site, with separated accounts and forums. The point is, we want to do more. The good point about our system is that's very easy to use, but we could love to ear what are in your opinion the killer features of this kind of services that no one implemented already (it's ok if it is very hard to implement it). Thanks for any feedback. p.s. I understand HN is not exactly a place were there are a lot of possible users for our service so it's very hard to do feedbacks about it.