As with embroidery samplers, before published compendiums of crochet and knitting stitches were readily available, crocheters and knitters
made samplers of crochet/knitting stitches. I have seen/collected "early" (c1850-1940)
Most early crochet and knitting samplers tended to be made up of lacy stitches, however some are made up of more dense stitchery.
Pictures and information on lace and crochet samplers can be found in Annie Louise Potter's book, A Living Mystery: The International Art & History of Crochet, 1990 A.J. Publishing International. Pictures and information on crochet samplers can also be found in Lis Paludan's book, Crochet History & Technique, 1995, Interweave Press, Loveland, CO. The May/June 1997 and JulyAugust 2010 issues of Piecework Magazine also has articles on crochet samplers.
There is a lot of misunderstanding about what crochet/knitting/lace samplers are. Samplers are samples of numerous different stitches, originally made to be referred to to replicate those stitches. I see many "crochet samplers" selling that are actually filet crochet figual designs, sometimes replication of embroidered alphabet samplers. Although they may be attractive they are not true samplers. More recent crochet and knitting samplers have been made into afghans, scarves, jackets, bags, and other useful items. Although they are not samplers in the traditional sense (ie. being made for reference of stitches), they are made up of numerous stitches/stitch-patterns and are used to hone and/or showcase their maker's skill.
I recall seeing knitting samplers in what I call the roll form, presumably Germanic. One of my book-form samplers includes tatting samples. Other lace samplers also were made. During roughly 1900 pillows and other items were made with crazy-quilt-like patches of various laces, but these were used as decorative items rather than references for lacework.