I've been working on a filet crochet project (I'll show you on Monday) and realized that you hardly hear anything about that form of crochet these days. Basically it's making squares in a grid with double crochet stitches and then filling in some of those squares to form pictures. The technique has been practiced since at least the 1500's as one way to make lace. It was popular into 20th century and often used to make tablecloths, table and dresser scarves, antimacassars for chairs and sofas, and doilies.
Caroline Ventura has some wonderful photographs of Portuguese altar cloths on her website that are definitely worth a look.
If you think this is something you'd like to try, stay tuned! I'm working on a beginner's tutorial. (Edit: It's up now here!) If you want to give it a go before then, Crochet Pattern Central has a nice list of free pattern here and it's not very hard to figure out on your own.
Happy Creating! Deborah