Everyone knows about Google and their free web based email called Gmail. The service was launched with a lot of marketing actions and was 100% free from the start but one could only create a Gmail account through special invites. If you knew someone who had a Gmail account, you could request them to send you this invitation. In those early days, Gmail accounts were so coveted that invitations were being sold through ebay.com auctions. The high demand for Gmail email address was also because the service offered 1GB (gigabyte) storage space for emails at a time when all the others were providing only a fraction of that. Anyway, after a few years, Google opened the doors of Gmail for everyone... so you didn't need a special invitation to create an account.