Gmail now has a new feature of sending out meeting invitations. This works exactly the same way as your windows based email client like Outlook etc.
Your friends can share their schedules with you in Google Calendar, and when you want to see a movie with them, you can check to see which nights they're free before sending out an email about it.
The calendar feature is now integrated with Gmail.
To find the availability of your friends and send out an invitation, do the following:
1) Start composing an email.
2) Enter the email Ids of your friends in 'To' field of the mail.
3) Click on 'Invitation' link as shown in this figure:
4) This will open up the Gmail calendar with the availability of your friends.
Here you should specify:
What: The Meeting Topic
When: Although there is a default time specified by gmail when the pop up gets opened, you can specify your own time and the system will recalculate the availability for all your friends.
Where: Location/Venue of meeting
Calendar: The calendar with whom the other person's calendar should be compared. Generally it will be the meeting leader's calendar.
Description: Something about the meeting or you can specify the meeting agenda here.
The light green portion shown in figure represents the time frame for which you are trying to look for their availability:
5) Once done, just press the 'Insert Invitation' button to send the invitation.
6) Here is the sample invitation copy which is received by meeting invitees:
Image and content source: gmailblog.blogspot.com