Crowdfunding, for the most part, is an exercise in pure capitalism. Entrepreneurs and resourceful individuals have an idea or product and digitally panhandle for funds, often raising thousands (or millions) of dollars in the process.

But there's a place for charitable giving in the crowdfunding world as well—and it can be lucrative for both nonprofits and individuals in need. Crowdrise, Fundrazr, YouCaring and GiveForward all focus on charitable efforts.

Given the wide swath of sites focused on doing good—and the policy by some not to rank their campaigns—it's tough to assemble an authoritative Top 10, but after a deep dive of several sites, here are 10 of the biggest we've come across that are making a difference. Their causes run the gamut—from working to fight Ebola to helping the homeless and victims of the Boston Marathon.

Considering now is the season for charitable giving, here is a look at how leading causes are getting the attention of people who want to do good.

A 2012 charity drive, which used crowdfunding and Facebook to help raise money for Save the Children on FundRazr, was sponsored by the gaming community AtheneLive. Together with DC Entertainment, which matched the donations of users, the group raised more than $1 million for at-risk children in the Horn of Africa in a single campaign.

AtheneLive has since launched its own crowdfunding platform—GamingforGood—which offers digital downloads of games in exchange for charitable donations. So far, that site has raised another $20 million for Save the Children.

Of late, the nonprofit is trying to fund an Ebola Children Relief Fund to save lives and protect orphans. The goal is to reach 3.5 million people.

This annual running event has raised millions for charity in the past, as many runners complete the 26.2-mile course for a favorite cause. This year the race is encouraging participants to crowdfund their run, offering anyone who raises $50 or more the chance to win two seats in the finish-line reserved section. The turnout has been impressive. With three days left in the campaign, it has raised more than $13.6 million for a wide variety of causes.

Natural disasters tend to result in donation spikes to the Red Cross, but the organization is consistently seeking donations. Through Crowdrise, it has raised nearly $4.7 million with both campaigns of its own and from people seeking to support it. Crowdrise doesn't have an exclusive relationship with the organization, though.

The Red Cross has used several other crowdfunding sites, including Indiegogo two years ago, when it was raising money for relief efforts for victims of Hurricane Sandy.

Since 1988, the Robin Hood Foundation has battled poverty in New York City, distributing more than $1.25 billion to soup kitchens, schools and homeless shelters. Three years ago it dipped its toes into the crowdfunding waters with Lady Gaga for a fundraising drive. It liked the results and began working with Crowdrise, where it has since raised more than $2 million.

Patrick Downes and Jessica Kensky were both severely injured in the 2013 blasts at the Boston Marathon, both losing part of their left leg below the knee. A friend, learning of their injuries, posted their engagement photo online, and it quickly went viral, capturing the public's collective heart. A fundraising site was set up on Giveforward.com, which collected more than $890,000.

"As equally overwhelming as the evil that day was how incredibly good these people were," Kensky told the Boston Globe earlier this year. "How do you thank people for this? How do we deserve this?"

This charity, co-founded by "Survivor" winner Ethan Zohn, has raised more than $740,000 on Crowdrise. The money, like that of many corporate-focused campaigns on the site, comes from a wide swath of smaller campaigns (often charity-focused marathon runners) who want to help the group, using soccer as a tool to help raise awareness and prevent the spread of HIV among children in Africa.

An open-sourced science project that seeks to learn more about the microbes in our stomachs, skin and so forth, isn't exactly sexy stuff. But it's just curious enough that this fundraiser, which goes under the name American Gut, has managed to raise $613,000 so far (and the campaign is still ongoing).

The donor perks—which include DNA extraction and RNA sequencing of donor's stool (yep, really)—aren't any sexier than the base study, but they straddle the line of gross and fascinating, which encourages people to give.

The sudden death of their daughter earlier this year blindsided Ian and Mackenzie Sandler. The 9-year-old suffered respiratory arrest during her last night at camp. The Sandlers channeled their grief by establishing a charity to help promote the health and welfare of children in need—with Riley's name at the forefront. The ongoing campaign has already raised $562,000 from friends, family and a lot of strangers who are captivated by the stories and bunny-eared smiling face of Riley.

"We could never have imagined that we would have over 900 supporters in less than three days," the Sandlers said in a statement on the page. "From our dearest friends to people we have never even met, your words and donations continue to touch and inspire us."

Crowdfunders, it appears, respond more to human suffering than the planets, but that's not to say they don't have a little green in them. The Nature Conservancy has raised just shy of $425,000 on Crowdrise, largely through supportive campaigns from marathoners and bike-tour teams.

Major Thomas Kennedy was killed by a Taliban suicide bomber in August 2012 while on foot patrol in Afghanistan, leaving two small children fatherless. Friends quickly mobilized and set up a crowdfunding site to establish a private trust for the twins. Word of the site spread quickly, and it ended up raising more than $400,000 for the family.