It's called the OAR, het Open Archief van OE-publicaties and it hosts not only that monograph, but many others and lots of archaeological magasines. You can search the database (though in a limited way) and get a short abstract for each item on the list, sometimes in English, mostly in Dutch. The Festschrift seems to be one of a few items mostly or completely in English, but if you are interested in archaeological results from Flanders, this is your database.
And I find it utterly amazing that things like it exist, just like that, free for everyone, on the Internet!