iOS: There's no shortage of great calendar apps to choose from on the iPhone. If you're looking for something a little different, the Tempo Smart Calendar combines a traditional calendar app with a personal assistant that extracts stacks of relevant information.
Tempo works a little like Google Now, providing you with extra information and context inside the calendar itself. When you create appointments, Tempo Smart Calendar scans your contacts to provide more information about the event, the people who you're meeting with, and where you're meeting. In a lot of cases, Tempo is also smart enough to add in email attachments to meetings when the meeting is mentioned, as well as include a list of contacts who will attend.
The app rolled out in the US and Canada in February; Australia and New Zealand are the first countries to be added to the service since launch. Localisation for each country requires the ability to recognise address patterns, phone numbers and common colloquialisms used in appointments.
The one potential limitation is that everything is done server-side, so you will be storing all your information on Tempo's servers instead of on your phone. That said, if you're looking for new calendar app and like the idea of accessing context and information before you even realise you need it, Tempo is worth a look.
Tempo Smart Calendar [iTunes App Store]