Romanian point lace is a beautiful art form. It is made by creating some kind of picture or pattern from a crocheted cord and then weaving a design from thread between the cords, with the woven design attaching to the sides of the crocheted cord. There are many different types of cord made for this purpose, but the simplest of them just involves single crochet.
Single crochet Romanian cord, if a little fiddly at the beginning, is both easy to make and incredibly versatile. I have used it to make frog closures for garments. Practical Crocheter has used it to make simple cufflinks. It can be used as decorative trim, to make simple jewelry, or even garlands, and it can also be used in any context where one would otherwise use knitted i-cord. It is certainly a sturdy alternative to a length of chain stitch.
I've only really used that basic, single crochet Romanian cord. I would like to play with some others eventually, as many are very pretty, but the basic one generally answers my needs. If you want to learn some of them, Elena Rugal Studio on YouTube has an entire playlist of tutorials for different Romanian cord types.
That said, the basic concept of Romanian cord doesn't limit you to single crochet. I've been playing around with using the same technique on half double and double crochet, and both work well. They are slightly wider and flatter than the single crochet version, and the overall look is different, but both work just fine.
The swatch at the top is the single crochet version, which has a very regular appearance. The middle swatch was done in half double crochet, and I like that it has an almost herringbone appearance. The bottom swatch used double crochet, and it really looks like an elongated version of the single crochet cord.
Since they use taller stitches, both the half double and double crochet versions work up faster than the single crochet version. However, they are a little more fiddly to start and have a pointed look at the end, so I did the first and last stitches of each sample in single crochet.