Making cards into tags is something I've done before. The really, really pretty ones you could cut out a shape around the image you want to save and make it into a simple ornament to hang on the tree.
I've also seen folks decoupage a collage of images onto trays, etc.I think that "might" work with Christmas cards - the paper might be too thick for that though?
When we were kids we reused Christmas cards to make paper chains and paper lanterns to use as decorations.
I too make home made gift cards out of Christmas cards. In the past I have made book marks and given as stocking fillers for the following year.
I frame some really nice ones to use a decor.
A work colleague uses card to make small gift boxes, I will try and find a link.
I’ve never done anything with my cards. I have saved a few through out the years. Now I have some ideas what to do with them. I like the origami boxes.
When I was a kid I remember in art class cutting them all into Octagons and piecing them together like a quilt to make a place mat, which the teacher then laminated. They were actually really nice....I had mine for years.
Now that so many of the people who used to send me cards have passed on and the younger people don't tend to do it so much, I keep some of the older ones to put out with the ones I get each year. It seems fitting to have cards out from loved ones who aren't around anymore at Christmas.
I have framed some, you can use a scallop punch and then glue the picture onto the plastic snowflakes that you can purchase at Dollar Tree. They come clear or in blue. Gma would cut a picture out and then punch holes around it and crochet (3 dc in each hole) around and put a string and tassel for a bookmarker.