These are the first of their kind I have come across in real life, and was super excited to find them--in part because they are great looking blocks sets, but especially because of their historical significance and rareness. There is a terrific website dedicated entirely to these - www.froebelblocks.com--from which I've lifted to the following text, written by Scott Boltman:

When Friedrich Froebel established the first system for educating young children, he created a series of playthings to provide children with focussed educational experiences. Up until that time, toys were intended for amusement and education was provided through books and instruction. Froebel's Kindergarten used play as its engine and his Spielgaben ("play gifts") were the fuel. During his lifetime he codified the series of Froebel Gifts up through Gift 6. After his death in 1852, his followers extended the series of educational toys by numbering other materials used in his school.