The last time I posted this message, I had two and later five invitations to give out. I got dozens of requests before I posted a note that they were all gone. Luca Filigheddu has seen this effect even more than I.
I appear to have received 999 invitations sometime yesterday! I don't know how long this will last, but I've already sent out more than two dozen invitations to some of the people who responded to my earlier post.
If you are interested, send me an email at firstname.lastname@example.org, listing your first name, last name and email address (that's what the current Joost invitiation form requires). Assuming my 973 remaining invitations don't suddenly disappear, I will try and get you invited within a day or so of your email.