A Grader blade or Earth leveler (as called by some manufacturers) is a blade mounted on a tractor (usually on the linkage) to level out ground as a basic grader. They are generally not designed to rip up compacted ground but to spread out loose material such as earth or crushed stone and hardcore to forma track.
The grader blade is a simplified design that evolved from the early towed graders designed for horses that was adopted for early crawler tractors and the basic leveling device created by using a plank towed by horses to 'knock' the tops off mounds of earth that had been tipped from a cart or rutted up by waggons padding.
When Harry Ferguson added the hydaulic linkage to the tractor the ability to raise and lower tools was quicly adaped for many tools other than just the basic plough and cultivator.
The old trailed horse grader design also evolved into the basic Motor Grader by bolting the trailed grader frame to a tractor directly & removing the tractor front axle.
Other light powered graders were built for maintaining dirt tracks by fixing the blade under the tractors body were the weight helped it cut deeper.