I love this idea. An envelope guest book. You just take a store-bought scrapbook/album and glue envelopes into it. Lay out colored pieces of paper for guests to jot notes down on, and then they can place them in the envelopes.
Faire-part de Mariage "Champêtre" en Letterpress et dorure à chaud Cuivre sur papier Kraft, accompagné de son invitation Dîner et d'une étiquette Dress Code /// Rustic Wedding Invitation in Letterpress and Copper Hotfoil on recycled paper, with Dinner card and Dress Code Tag