For those who are already using Lync (hosted On Premises or Online) but have host online meeting with people without the Lync client, you may notify them to download the Lync Client Attendee.
This will offer them the same user experience than with the Lync client but without the need to have a Lync user account (On Premises or Online).
Go to http://www.microsoft.com/download/en/details.aspx?id=15755 and enjoy