The word "resume" can be used pretty loosely these days. The word no longer refers to a tangible piece of paper with a list of credentials and accomplishments on it. Instead, users are relying on portfolio websites, social media profiles, and online personal brand reputations to do the heavy lifting for them. Still, when I use the word "resume," I'm referring to that list of credentials and accomplishments--no matter how you choose to format, publish, or display them. A broader, more diversified resume is a sure way to increase your job prospects, fish for a raise, or even get promoted from within your own organization.

Thanks to the resources and information available online, it's no longer necessary to expand your resume with expensive classes or further formal education--instead you can use free methods like these to sharpen or add to your skills:

1. Attend online classes at Coursera. It's amazing how much information is available for the taking on the web. Dozens of online platforms, Coursera being only one of them, now offer tens of thousands of interactive classes that can be taken by anyone, online, for free. Many of these classes are offered by major universities, and cover topics from Accounting to Music Theory to Computer Programming. The format varies based on the platform and class you choose, but the bottom line is almost always identical. Spend some time watching videos, reading course materials, and engaging with other users in discussion. You won't have to study for finals and you won't always get a formal certification, but you will walk away with new skills, new knowledge, and a new line for your resume.

2. Go through tutorials at Codecademy. I list Codecademy here because it's one of the best platforms around, and it covers a range of in-demand skills related to computer programming, but programming and coding aren't the only tutorials available on the web. Codecademy distinguishes itself from Coursera and similar "course based" platforms because it's all based on interaction and practical application of skills. That is to say, rather than reading up about how to code, the system will guide you through real coding exercises until you get the hang of it. Most people learn better this way.

3. Look for YouTube videos. YouTube is useful for more than just funny cat videos and watching people prank each other. A quick search for almost any skill can leave you with a selection of at least several dozen videos, ranging in complexity from a student's 5-minute presentation, to a series of hours-long videos from Ivy League school professors. It's worth your while to dig through the fluff and find the valuable lessons underneath. A few hours on the right YouTube videos can earn you a new skill (as long as you practice it once you've acquired it in theory).

4. Network with professionals on MeetUp and LinkedIn. One of the best ways to learn new skills is from people who already have them. Utilize social networking sites with a professional slant like LinkedIn or MeetUp, where you can join niche groups for regular meetings. For example, you might find a group of accountants during tax season discussing various problems or a group of coders trying to advance their skills. Join one of these groups (or a Group on LinkedIn) and start getting involved in these discussions. If you stay committed, you'll eventually build your skills to match those of the other group members.

5. Volunteer (and become a board member). Volunteering is completely free because most organizations are begging for volunteers. Depending on who or what you volunteer for, you can probably get in touch with some of the organization members. After putting in some requisite time, you can usually work your way up to becoming a board member or some similar position of authority within the group. This method of resume building isn't about building a skill; it's about showing your commitment to the community and adding another credential (plus, you'll earn more professional connections, and that's never a bad thing).

6. Become a speaker or organizer. There are probably professional events happening in your city every week. Sign up to be a speaker for an event that fits your niche--it might be industry related or community related. Doing so will increase your reputation in the area, and gives you a little extra line to include on your resume. Like with volunteering, if you do this enough, you can eventually work your way up to a position of higher authority, in this case serving as an organizer for the event.

7. Talk to people in other departments. One of the simplest ways to increase your skillset for free is also one of the most overlooked. The next time you find yourself bored or wandering around the office, talk to someone in a department adjacent to yours. You may find yourself learning more about the company or learning an entirely new skill. More perspective won't always improve your resume, but it will allow you to speak more intelligently about broader business problems, and give you more experience in working as a team. Never pass up an opportunity to find out more about a coworker's role in the organization.

These seven strategies are only the beginning. It seems like every day, dozens of new resources pop up for public consumption. Remember, your skills are a resource that add value to yourself as a worker. The more time and energy you invest in yourself, the more valuable you're going to become to your current (and future) employers. Thankfully, that investment requires little to no money these days--all you need is time and commitment.