Summer of Design is a free 12-week design course, delivered to your inbox. Taught by friend of Lifehacker and author of Design for Hackers, David Kadavy, the course takes a "reverse engineering" approach to understanding how design works.
The course is similar to previously mentioned Hack Design (where Kadavy is a teacher), but based on the Design for Hackers book. (The book is not required for this course.) The first weekly email starts on June 4 with "Why Design Matters".
Other lessons cover topics such as typography, colour theory, and composition and design principles. Emails include quizzes and are supplemented with discussions on the Design for Hackers Facebook page.
The free course may never be offered again (or offered for free again), and enrolment closes on June 3. So if you'd like to get design lessons delivered to you and bump up your design knowledge, hit up the link below to sign up while you can.