Instead of back and forth emails for every meeting, with Vocus.io you can share your availability and poll the invitees in a single message. The content of the poll will automatically change to show responses from each invitee, allowing everyone to know who's-available-when without the usual infinite thread.
Each meeting pool will automatically refresh to show the latest responses from invitees. For example, let's say you sent a meeting invite to Person A and Person B. Person A responds within five minutes and Person B opens your email (say, after an hour), they will see Person A's response within the same invitation block - Vocus.io allows you to transform email from being a static medium to an interactive medium, that users can interact with and change over time.