In the 1960s, the designer of the modern Lego brick formed a new company to make a product for adults called Modulex.
In the early 1960's Godtfred was building a new house and, naturally, he tried to model the structure with Lego bricks. The problem was that the Lego brick, with an aspect ratio of 6:5, was different than standard European construction modules of 1:1. Rather than contend with the problems of using regular Lego bricks he simply had new, special bricks molded for him. Bricks that would allow him to more closely copy his architectural plans.
The blocks were intended for use by architects. Reference Library has another look at these Legos for grown-ups. (via things)