Flexi-Block was a clone brand that was made in or around 1988 by Fantasy Toys, Inc. They only had 4 different parts: a 2x2 brick, a 2x4 brick, a wheel, and a 2x2 axle holder brick for the wheel. They are a different size than LEGO bricks, and thus are incompatible with the LEGO system of play.
The 2x2 and 2x4 bricks only came in four colors: red, blue, yellow, and green. The wheel and axle holder only came in one color: black. Unlike most clone brands, they have one advantage over LEGO. The bricks can snap together with a system of pegs and notches on the side of the bricks (except, of course, the axle holder brick, which has no pegs, only notches, and the wheel) that allows them to flex, hence the name.