"at Home" cards are distinct from invitations in that they have less information.  They can simply have the words 'at Home' in the centre of the card (please note lower case 'a' and upper case 'H') with the R.S.V.P towards the bottom left of the card. This enables as many or as few to be used at any events at any time.

You can add a name at the top (Mrs John Assheton) above the words 'at Home' and below, leave blank to fill in a date and a venue. You can also fill in an address and/or email address under the R.S.V.P.

If you want more information than this on the card it becomes an invitation.