It is only for Passover. Christ's last supper was a seder, or Passover meal. Passover falls on a different day each year, sometimes falling before, sometimes after Easter, but always around the same time.
However, it occurs twice a year, not once, on consecutive days. families have a choice of which of the two days to celebrate, and the ceremony is exactly the same. I was told that the reason for this is to allow for time differences in different parts of the world. Some families repeat the seder on both days.
It is very much part of the tradition to invite to the seder not only friends and relatives, but anyone that you know who has nowhere to go onthat day, including those who are not Jewish. In fact there is a part of the ceremony where someone goes to the door and invites any passer-by to come in and share the meal. This is rarely taken litrally now in the US, but I have known people who were invited to participate in this way.