Much has been written recently about the bonuses and challenges of managing Millennials (a.k.a. Generation Y). Regardless of your feelings about them, these people will account for 75 percent of the global work force by 2025. But attracting and retaining them will be a tricky thing for companies that try to operate in the same ways they always have. Not only do Millennials want autonomy, fun, and flexibility in their work, they value working for companies with a social mission. In short, they'll take meaningful work over money.

But what if your company isn't involved in saving the planet or other noble pursuits? Take some cues from three companies that have come up with creative ways to give workers purpose.

Appeal to their green side by incentivizing them to live near the office.

Messaging company offers its 18 employees a $500 monthly stipend if they live within five miles of its Palo Alto, California-based location. Co-founder Georges Harik sees several benefits for both employees and the company. Not only can employees feel good about contributing less to traffic and pollution, they're more likely to walk or bike to work, which brings obvious health benefits. They're also more inclined to get to work earlier and stay later when they don't have to factor in a commute, while at the same time sharing a neighborly bond.

"We really want to all be in an area where you can run into people you know from work outside of work," Harik says. "It's a pretty nice community-like feel."

Send them around the world to see philanthropy in action.

Better World Books started 10 years ago with a campus book drive and since then has grown to be a $63 million company that sells books online collected from about 4,000 libraries as well as campus book drives and book drop boxes in communities around the U.S. With each book sold, the company donates another, along with a portion of the sale, to one of its nonprofit literacy partners.

"Basically, we're a very mission-driven company with our triple bottom line, and it's part of what draws people to us as a company...But we're not sitting teaching kids to read. We're not actually driving donation loads of books and handing them out to people who need them. That impact really primarily happens through our nonprofit literacy partners, and so there is a tendency to feel separated from the mission in your day-to-day work," says chief literary officer and VP of marketing John Ujda.

The company's solution: Every year it sends eight employees to another continent to see firsthand how the nonprofits it supports are helping people in impoverished countries learn to read. In January, Ujda took a group to Zambia for 10 days, although previous trips have included jaunts to Cambodia, Peru, Chile, Brazil, and various African countries.

As for how the employees are selected, Ujda says every employee who has been with the company for more than two years and performs in the top half of his or her area is put into a lottery, with one entry for every year of service. "It's kind of an exciting day when that happens," he says.

Give them money with which to do good.

Nearly all of GiveForward's 25 employees are Millennials, so it makes sense the fundraising website is nailing the concept of providing meaningful work for younger workers. The platform gives its users a way to raise money to pay for medical, vet, funeral, and disaster-related expenses. GiveForward gives each employee $500 a year to spend on people who they feel truly need it.

You can see how this would be fulfilling: A GiveForward fundraising coach recently mailed a cape to a three-year-old boy with a penchant for superheroes but battling cancer, while another team member took to giving money and Starbucks cards to a homeless man who often sells StreetWise magazine outside GiveForward's building in Chicago. Other gifts include a Christmas tree sent to a couple living in a hotel because their home was destroyed in a tornado, a travel care package sent to a woman with cancer who had to travel across the country every three weeks for treatment, and a package of new toys sent to a little girl whose own were destroyed in a fire.

The idea for the CUJ program, which stands for "Create Unexpected Joy," came from a team member who said it only made sense considering the company pushes its employees to make decisions and take initiative through its "Be the CEO of your position" mantra.

Ah, autonomy--another thing Millennials appreciate.

Co-founder and president Ethan Austin says the company's retention rates are "great," and in the six years GiveForward has been around, people have mostly stuck around, sometimes even in remarkable ways.

"We bootstrapped for the first two and half years, and we didn't actually pay ourselves anything," says Austin, adding that the company's first employees were two interns who started with three-month gigs but then never left, even though GiveForward couldn't pay them until the year-and-a-half mark. "I think they were very interested in the mission of what we were doing, but then we also made it fun. We made work the place where they wanted to be."