One of the great things about the internet is the way it can bring together people who otherwise would not have been in touch with each other.
Pledgebank(www.pledgebank.com) is one of the latest and most interesting ideas of this sort to be launched.
Anyone can sign up for free at the site to make a public pledge about anything that matters to them.
With Pledgebank's help, people can attract supporters, turning a one-man mission into a powerful and popular campaign. For example, you could sign up and say you will write a letter to your MP about the threat of the closure of your local hospital, but only if 200 local people will do the same.
Your pledge becomes a web page where you can outline your promise and your reasons for making it. It also provides an opportunity to persuade others to join you.
Because it is a web page, it is easy to spread the word.
You can email your friends and contacts to ask them to visit, and encourage them to forward your request to people in their address books.
Successful pledges catch on quickly, especially on matters important to small communities.
Each pledge can be as simple or as ambitious as you want. It could be as simple as promising to pick up litter in the street, or signing up to be a blood donor. Pledges can be political, environmental, or just a bit of fun.
Each pledge can be customised. You, the creator of the pledge, can decide how many people you want to join in and a deadline for the target.
If you reach your total number of pledge supporters by the date set, everyone who signed up should fulfill the original promise. If the target isn't met, no-one need do anything.
The idea has proved extremely popular. Recent successful pledges include a boycott of a supermarket chain, a plan to start a book club in London, and a 40-year-old man's idea to dye his hair blonde to raise money for charity. More than 150 people signed up for a pledge to complain to the Parliamentary Commissioner for Standards about George Galloway's Celebrity Big Brother appearance.
Of course, just because people have signed up to your pledge, it doesn't mean they will do what they've promised. But Pledgebank has found that, in pledges involving donations of money, about three quarters of supporters pay up.
The idea has caught on in high places, even Tony Blair has created a pledge. On the website, he has written: "I will become the patron of a London community sports club. I will work with the club over the years as the Olympics approaches in 2012 to support their development and raise their profile but only if 100 other public figures in London will join me in supporting other clubs."
The deadline to join him is July 25. Visit london.pledgebank.com/Sportclubpatrons for more details.
Pledgebank was created by MySociety and a team of volunteers, many of whom were also responsible for Fax Your MP (re-named writetothem.com). For more information about MySociety projects, visit www.mysociety.org.