Unable to get out to buy birthday cards, I have recently been making my own, and am managing to use all manner of crafts to make them.
My latest creations have incorporated string art and embroidery on card.
I have also stitched some little blackwork (though not actually in black) motifs that I can use on cards.
Paper quilling.
Paper cutting
Cards with applique pictures machine-stitched onto them.
Glass painting.
I've used all these and more ?
While I haven't done it yet, I have also thought of crocheting fine motifs to decorate cards.
As yet, I haven't thought of a way to use knitting on them, but luckily one DiL actively encourages me to knit clothes for dgd, so I can knit whenever I feel like it. Knitted soft toys have always been appreciated by all my DgC too.
I know one Gransnetter was very disparaging on another thread about handmade cards, making it clear that she doesn't like to receive them, but luckily most people don't seem to feel that way.
I enjoy making them, and while it's a bonus if a recipient genuinely appreciates their card, I don't expect them to keep them for ever. Like someone up-thread, I have had my pleasure in the making - any more than that is a bonus.