GAP Years can be a time of personal insight, an exploration of probable future careers, or simply a way to recharge in a meaningful way.  A GAP year is typically taken between high school and college to deepen practical, professional, and personal awareness.  AGA continues to advance the field of GAP Years by collaboratively pioneering research on its benefits, as well as serving as an information and advocacy hub for university admissions personnel and educational counselors. 
https://www.gapyearassociation.org/

AmeriCorps NCCC is a full-time, residential, team-based program for young adults, age 18-24 (with no upper age limit to serve as a team leader). Members develop leadership skills and strengthen communities by completing service projects and gaining life experience.  
Teams, comprised of 8-10 members, complete multiple projects that address essential community needs throughout the United States. During the 10-month service term, members receive lodging, transportation, uniform, and meals. Upon the completion of the program, members are eligible to receive the Segal AmeriCorps Education Award equal to the maximum Pell Grant amount.

https://americorps.gov/

AmeriCorps VISTA members serve full time (~40 hours/week) for 1 full year at a community organization (nonprofit, college/university, local government office, etc.) on anti-poverty projects. AmeriCorps VISTA members work on projects that build the capacity of their organization. Projects can vary and are not limited to: developing outreach and marketing campaigns, building a social media presence, creating a program database, writing grants, managing a program in its first year, and recruiting volunteers. If you are interested in developing a certain skill set, working on a specific project, exploring a certain career path, start your AmeriCorps VISTA application here: https://my.americorps.gov/mp/login.do

Put your idealism to work through AmeriCorps. Make a community safer. Help a kid get a real education. Protect the environment. Whatever your interest, there's an AmeriCorps program that needs your courage, your skills, and your dedication.  AmeriCorps is a network of national service programs that engage more than 50,000 Americans each year in intensive service to meet critical needs in education, public safety, health, and the environment. AmeriCorps members serve through more than 2,100 nonprofits, public agencies, and faith-based organizations. They tutor and mentor youth, build affordable housing, teach computer skills, clean parks and streams, run after-school programs, and help communities respond to disasters. Created in 1993, AmeriCorps is part of the Corporation for National and Community Service, which also oversees the Senior Corps and Learn and Serve America. Together these programs engage more than 2 million Americans of all ages and backgrounds in service each year.  Must be 18-25 years old. https://www.cityyear.org/

A gap year is a unique opportunity to break free before college and discover the world – all at your own pace.  Touch down in one of nine destinations, where you’ll learn to navigate and appreciate all that another culture has to offer.  Spend a semester or a full year making discoveries large and small.  Build a foundation of language and intercultural skills that will last a lifetime.  18+ years old https://www.ciee.org/  

A NOLS gap year is a unique experience where you’ll get hands-on leadership practice through a wilderness expedition. You’ll finish your gap year well-prepared to take on whatever challenges life throws your way in college, your career, and beyond.  17-19 years old 
http://www.nols.edu/gap-year/ 

Conservation Internships:  For those 18 and older. Live and work with resource management professionals at natural and cultural sites nationwide. Internships available throughout the year in all fields; terms from three to twelve months. Expenses paid, plus living allowance, travel grant.  Conservation Corps:  Also for those 18 and older. Trained and supervised by SCA staff, Corps of ten or more provide specialized conservation services in rustic, residential setting. Service terms like Conservation Interns. 
http://www.thesca.org/ 

Come see what the world has to teach you. Go to class while sailing at sea, watch the sunset over the Indian Ocean or stare up at the Mediterranean stars.  Whether in class, studying, or engaging in shipboard activities, you’re always a few steps away from friends, the ocean, and a global perspective. Must be 18 years or older. 
http://www.semesteratsea.org/ 

The National Youth Science Camp (NYSCamp) is a residential science education program for young STEM enthusiasts the summer after they graduate from high school. Students from around the country (two are selected to represent each state and Washington, D.C.) are challenged academically in exciting lectures and hands-on studies, and have voluntary opportunities to participate in an outdoor adventure program, gain a new and deep appreciation for the great outdoors, and establish friendships that last a lifetime.  
National Youth Science Camp please go to: https://nysf.smapply.io/h 

UnCollege helps students identify areas of interest, accelerate their learning, and be happy at the next stage of life.  This 9-month program begins with living and volunteering in 1 of 5 countries, attending workshops and build a portfolio for 10 weeks in San Francisco, and culminates with an internship that matches your professional objectives.  18-26 years old. 
http://uncollege.org/ 

As a recent high school graduate 18 or older, YFU invites you to spend a 13th year abroad. Bridge the gap to your future, discover the real you, and experience the world. Whether you've just graduated, deferred college admissions, or are deciding what's next, you can gain from an increased understanding of another culture, benefit from the unique strengths of academic institutions abroad, and become part of a global family.  It takes a special kind of person to consider living and studying abroad as a Youth For Understanding USA student – one who is both eager to travel and willing to take an active role in his or her own education. 
https://study.yfu.org/