There are a variety of alternatives to the traditional guest book, below are a few of my personal favourites
Why not get your guests to write personal wishes on some pebbles
I love this fingerprint tree - guests simply make a fingerprint leaf and write their names, these can be purchased in kits.
A beautiful pear jar that doubles up as a cookie jar after the wedding, these and more fun ideas can be found at https://www.pinkfrosting.com.au/shop/
a great idea, get your guests to write on a brick of the game jenga
A wishing line
Ask your guests to sign a photo frame, this can then be used for your favourite wedding day photograph later on
Wishing trees, i love this idea, they are simple, can be created for a low budget and tailored to your colour scheme. You could add crystals to the tree for an extra magical effect.