iOS: Free-Time is an unusual but helpful app that takes a look at your iPhone's calendar(s), figures out when you're free, and lets you know how much free time you have open in the day. You can then share this information with friends for simple planning.
Free-Time works with any calendar you sync with your iPhone, whether that's through iCal, Google Calendar, Microsoft Exchange, or any other supported service. When you start it up, it'll teach you how to use it and you'll enter a little information about your day so it knows when you're generally busy even though your calendar shows that time is free. These are things like going to work and sleeping. Once you answer these questions, you'll be presented with all the time you have available in the day. You can then apply filters to only show when you have time for certain activities, such as dinner or coffee. When you've selected a period of time you want to share, you can send it via SMS, email, copy and paste it wherever you want, or bump it to another device running Free-Time.
While the app seems a bit unusual at first, it's a neat idea that's executed well. When someone asks you if you're free on a specific day for a specific purpose, you can use Free-Time to check.
Free-Time (Free) [iTunes App Store]