It's an international network of people who are willing to let you stay with them for free just because you know Esperanto. It's like Couchsurfing but much older, and a lot of Esperantists take an extended vacation traveling around using it. Here's the website (which doesn't have nearly as many names as the little booklet): http://pasportaservo.org/
Tio estas tre bona! Dankon pro respondi al mia demandon. Mi vidas ke vi parolas la germanan kaj hispanan. Cu vi deziras konkurenci sur duolinog?