What's the secret to nurturing a healthy and active mind as you age? Never stop learning! Learning isn't just for the classroom; technology allows you to learn about a variety of subjects from the comfort of your couch. Here are several free and low-cost ways to continue your education outside of the classroom.

Coursera (coursera.org) is a massive open online course (MOOC) that allows people to take classes for free. It partners with universities and organizations around the globe to offer students courses in a range of subjects including the arts, economics, physics and more. Courses last several weeks and allow students to work at their own pace. Students can also elect to take courses within a signature track discipline and receive a verified certificate when they complete the program, for a fee.

Udemy (udemy.com) is similar to MOOCs in that it offers a variety of courses online. However, unlike MOOCs, the courses aren't tied to global universities and are taught by professionals in the field of study. Students are typically looking to increase their job-related skills instead of looking to fulfill college credits. Udemy offers both free and fee-based courses that allow you to work at your own pace.

EdX (edx.org) is another growing MOOC platform. As with other MOOCs, students can earn certificates for the courses they take for a fee, or audit the classes for free. Courses are divided into different levels, including high school and professional education courses, and are offered by universities around the world.

Skillshare (skillshare.com) is a membership-based MOOC that offers courses taught by proven experts in industries such as design, business, photography, etc. Like Udemy, students want to gain new skills either within a profesisonal capacity or as a hobby. Membership is $10 per month for unlimited access to more than 800 classes or $96 per year. There are limited number of free classes that are available as well.

LEARN FOR FREE

YouTube EDU (youtube.com/edu) features a large inventory of educational videos from a variety of sources, including universities and popular websites. Watch lectures and videos about astronomy, business, philosophy, mathematics and more. If a particular area of study interests you, subscribe to its channel so that you'll never miss an interesting video.

TED Talks (ted.com) have gained popularity over the last few years; however TED began in 1984 and stands for Technology, Entertainment and Design. It's a global community where new and interesting ideas are exchanged through short talks given by leading experts and professionals. Topics range from science and technology explanations to how to be happier.

iTunes U (Free for iOS) features a variety of courses, lectures, etc. from leading universities for free or a small fee. If you see a course that interests you, subscribe to it and the content will load into your iTunes library automatically.