15 Ways to Enhance Your Career (for Free) These newsletters, courses and podcasts will take your business game to the next level.

Once upon a time, going to graduate school was the key to moving up in the food chain, or equipping yourself with the skills and learning to run a company of your own. But that's a thing of the past. Today, you don't have to shell out the big bucks to pick up new skills or learn in the middle of your career.

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Now, we have the Internet. And this tremendous resource has endowed all of us with the resources to learn virtually any skill or subject: In fact, there's practically nothing standing between us and the knowledge we want to acquire -- regardless of how little time or money we have to spend. Consider the following wealth of resources just waiting for you to try:

Email newsletters that help you keep your ear to the ground

1. Hiten Shah's SaaS Weekly. This is the best newsletter around for anyone interested in SaaS. Each Monday, Shah delivers the best content from all around the web covering every aspect of SaaS, from pricing to product to actionable tips for any founder.

Hiten is an entrepreneur, startup advisor and all-round SaaS expert. He's founded multiple startups with million-dollar run-rates, including KISSMetrics and Crazy Egg, and shares his insights on SaaS and the tech world on his personal blog.

2. Mattermark's Mattermark Daily. Mattermark bills itself as the Bloomberg for tech. It's a powerful business intelligence tool for salespeople and VCs alike to find the startups they want to do business with. And, in addition to its data platform, Mattermark curates some of the best startup-related content on the web.

Its daily newsletter, Mattermark Daily, brings together the best content from startup operators and VC investors. That potent combination is why the newsletter has amassed more than 80,000 subscribers and become one of the most influential in tech.

3. Jimmy Daly's Swipe File. If you're interested in content marketing, then you have a lot to learn from creator Jimmy Daly. As head of content marketing for email marketing platform Vero, he grew the company's blog to over 100,000 monthly readers.

His personal newsletter, Swipe File, is chockful of insights, not just for content marketers, but for anyone who wants a weekly dose of creative inspiration and tips to work better. From general productivity tips to inspirational stories, Swipe File is well-curated content you don't want to miss.

Related: 5 Reasons Why Entrepreneurs Should Get Serious About Online Education

Massive Online Open Courses (MOOCs)

4. Coursera. Why go to one expensive college when you can cherry-pick courses from the top universities of your choosing for much cheaper? Coursera gives you the opportunity to do just that -- some of the courses are even free!

Whether you want to take Stanford's Intro to Machine learning, an HTML web development course from Johns Hopkins or a classical music course at Yale, Coursera has you covered.

5. Salman Khan's Khan Academy. Founder Khan was tutoring a few relatives in math when he had a huge breakthrough: Instead of teaching everyone at once, why not put the lessons on YouTube where everyone could watch on their own time line? Thus, Khan Academy was born. It's blossomed into a totally free, non-university affiliated library of courses in every subject you can imagine, from beginner to expert level.

6. OpenClassrooms. It's a common issue today. Tons of people want to work in the exciting world of tech, but don't think there's any place for them without engineering know-how. Enter OpenClassrooms. This is the modern vocational school, teaching pre-professional skills for today's world in topics like digital marketing, design and web development.

Teach yourself a cool new skill.

7. Codecademy. Codecademy offers automated mini-courses in all areas of coding -- from HTML to Ruby. There are no teachers, so users can go at any speed they want. But if they do get stuck or need help, Codecademy has a discussion forum full of fellow students willing to lend a helping hand.

8. Duolingo. The ever-increasing global connectedness gives us the opportunity to interact with people from all over the world. But what good is it if we can't understand one other? Now it's Duolingo to the rescue. The site offers courses in every language, from Italian to Arabic, to something as obscure as Irish Gaelic. Courses keep students engaged, with a fun, gamified system that gives users points for correct quiz answers. It's addictive and educational.

9. Yousician. Learning a musical instrument can enrich your life, but most people don't think they have the time for lessons. Yousician changes that with lessons for the guitar, piano, bass and ukulele. Upload any song you want to learn and get a step-by-step, interactive tutorial that provides instant feedback. Keep the rockstar dream alive!

Learn on the go with these podcasts.

10. The Startup Chat. On this podcast, Hiten Shah teams up with Close.io founder and sales expert Steli Efti to bring listeners actionable advice right from the startup trenches. The Startup Chat is required listening for any founder and would-be startup founder. Together, Hiten and Steli have backgrounds in all things startup -- the duo covers everything from building a remote team, to fund-raising, to delivering a kick-ass product demo.

11. Andreessen Horowitz's a16z podcast. Having backed heavy-hitters like AirBnb, Pinterest and Twitter, Andreessen Horowitz is one of the most prestigious VCs around. This podcast, hosted by a rotating cast of thought leaders from across the startup world, covers the macro topics in tech that will determine the future of the industry.

12. Dan Carlin's Hardcore History. On this podcast, historian, political commentator and radio veteran Dan Carlin explores world history in an accessible way. He's unconventional, puts himself in the shoes of the figures he explores and takes a "what-if" approach that makes for exciting theater of the mind.

Stock up your iPad with these free ebooks.

13. Revolunet's Collection of Python Resources. Revolunet offers you the chance to delve into one of the world's most-used coding languages, with this massive list of free Python ebooks. Python is one of the most versatile coding languages around, but with 60 ebooks to peruse, you'll find that there's no skill you can't learn here.

14. Fifty Shades of Growth. Growth-hacking is all the rage in the startup world these days, and with good reason: It's enabled companies like AirBnb and Uber to reach millions of users extremely quickly. This ebook draws from the best in the business, and has insights from experts like Brian Balfour Sean Ellis and Entrepreneur's Neil Patel.

Related: The Latest – and Unlikeliest – Man to Reinvent Online Education

15. Hubspot's Cold Email Hacks. Attention, salespeople! According to a recent survey, over 70 percent of people surveyed reported that they would prefer businesses to contact them via email. It stands to reason then, that if you want to close deals, you need to be a great emailer. Luckily, HubSpot has you covered, with this super-comprehensive guide to cold emailing. Overall, sales is one harshest, most unforgiving jobs out there, so salespeople are after any edge they can get. They'd do well to check out this free ebook.