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.
Froebel Gifts 2 through 6 (aka "the Building Gifts") are wood blocks in various shapes and quantities. Known most commonly as Froebel Blocks, these toys were made famous in the USA by the Milton Bradley Company. Milton Bradley himself was a strong advocate of the Froebel method. Josef Albers, Charles Eames, Buckminster Fuller, Johannes Itten, Paul Klee and Frank Lloyd Wright are famous examples of children educated with the Froebel materials.
These two sets are "Gift 3" and Gift 4", produced by Milton Bradley c. 1900. The Gift 3 box has its original label, and contains eight one inch cubes. The Gift 4 box no longer has its label, but contains 8 rectangular blocks, each 2 x 1 x 1/2". The boxes measure 2 5/8" cubed and feature slide tops and finger jointed corners. All are in very good condition, with just a bit of aging to the wood visible on the blocks. S. Hastings is written in pencil on the underside of one box.
I can't find any other sets out there more sale; mostly just photos of sets in museum c collections! Price is for both block sets together.