This is a Melissa And Doug Classic Toy Wooden Alphabet Truck Play Set that's produced by the good folks over at Melissa and Doug. They always make the neatest stuff for traditional toys.
The wooden alphabet truck is roughly 13 inches in length and 4.5 inches tall.
It comes with 28 letter blocks that slip onto the pegs for stackability. Each block also has a stamp of various animals and items related to each letter on it.