I use <a href="http://doodle.com/" rel="nofollow">http://doodle.com/</a> for appointments (as well as it's original purpose of polling a group for the best time for an event). For appointment slots, set the options: "Participant can only choose one option" and "Limit the number of participants per option" to one. No one ever needs to log in to anything unless they want to (for setup or responses). It also has fancy options for linking with calendars, but I've never used those.
I've switched to <a href="http://tungle.me" rel="nofollow">http://tungle.me</a> . It's a lot better, and it's free.<p>The appointment slots feature was just not solid enough - lots of weird bugs, the time zones sometimes got screwed up, and lots of double-booking.
This was extremely timely. I just got off a call where I was struggling how our team could communicate appointment availability with a third party. This is a great solution and you don't have to share personal/sensitive calendar information with others.
I'm surprised it takes more than 1 email each to pick a time.<p>Offer: Let's have a call. I'll suggest 2pm Tue. If that doesn't work, please let me know any time between 1pm-6pm Tue or 9am-11am Wed.<p>Response: 9am Wed.<p>I do think the gmail calendar approach is neater; the only downside being it requires the other party to use google calendar already.
Of course I learn about this great tip a week after I converted all my calendars over to iCloud. Does anyone know of a comparable feature in iCloud calendars?