I’ll take the liberty of writing about a project that I developed that run for 11 years successfully. I believe that this project could be executed today easily and have as much success as it did when originally developed.
Project Name: MathWorld Interactive
Project URL: http://mathforum.org/mathworld/ (Note: Project is no longer active but it was hosted at Drexel University and they maintain a page of the project including student work.)
Topic: The project was initially started in 1991 on FidoNet and was called MathMagic. At that time, all work was done on a message board and there were no graphics available. Over time, MathMagic became MathWorld Interactive. I wrote this statement which is featured on the site and it gives a good overview of the purpose of MathWorld Interactive.
The interactive site was dedicated to helping educators and parents motivate their students to solve open-ended word problems, communicate mathematically, and share cultural and geographical information. Participating were students from all over the world working on open-ended word problems (levels: K-3, 4-6, 7-8, 9-12) called MathWorld Interactive Challenges. The Challenge Cycle started every 12 weeks and the students followed a specific problem-solving format. (Mortensen, 2012)
The project was a huge success and was featured as a Yahoo Cool Site of the Day. Unfortunately, it became so popular that I was unable to maintain it on my own and still work as a teacher. When I finally had to shut it down, there 1500 participants in countries through the world. In addition, a spin-off site, GeographyWorld Interactive, was proving successful. At this site, students shared local landmarks with students around the world, as well.
True Story: I was a new teacher in 1991 and I was so excited to have the students in my middle-school class begin problem-solving and to have them think outside the box. The group of eighth graders basically stared at me as if I’d grown a third head when I requested they problem-solve. I knew I needed motivation and MathWorld Interactive was just the thing. The students would do very high-level problem-solving, writing out detailed strategies to share online, as long as they could ask a question of students in another country at the end of the strategies.
On one occasion, my students were problem-solving with students that attended an all-girls school in Australia. My students worked feverishly to being the collaborative problem-solving process on a problem, In how many different ways can you divide a square into 4 congruent shapes?, a seemingly easy problem that, when considered in depth, has amazing possibilities and encourages out-of-the-box thinking. The result was extensive problem-solving strategies with the following question added to the bottom: How can you stand going to an all-girls school? (In true middle-school language!) To this, we received a reply with tons of collaboration and extensive problem-solving strategies attached and modified and, at the bottom of the paper, the response to the question: Don’t worry! There’s an all-boys school around the corner. 
Whenever I visit it, I want to start up the project again because it was so successful for students. What do you think?
References:
Mortensen, C. S. (2012). Drexel university. Retrieved from http://mathforum.org/mathworld/
*Note: The idea behind MathMagic was originally that of Carol Mortensen and Alan Hodson. MathMagic Fidonet was the work of Carol Mortensen and MathWorld Interactive was solely the work of Carol Mortensen.
Carol Mortensen has nearly twenty-three years of educational experience. She began as a substitute teacher as she worked toward her degree. Upon graduation, Carol began teaching middle school Math and Algebra I and served as the technology liaison for her campus. She served as a teacher for 16 years and was lucky to have taught at Hillcrest Middle School, a 1:1 campus where every student was issued a laptop computer. She also worked as an Instructional Technology Trainer for her district providing training and technology integration support for campus and district staff, faculty and administrators. Currently, Carol enjoys her position as the Campus Technology Integration Specialist for Deer Park High School – South Campus. Before taking this position this year, she served for three years as the Campus Technology Integration Specialist at Fairmont Junior High in Deer Park Independent School District. In this position, Carol provides integration support and training to the students, staff, faculty, and administrators at the campus and district level. In addition, Carol is an online Math instructor for Aventa Learning and K12. The Texas Computer Education Association (TCEA) named Carol the Classroom Teacher of the Year for her innovative and creative use of technology to create a 24/7 virtual classroom using her classroom website. Carol has presented at school districts throughout Texas as well as state and local conferences on a variety of technology integration topics. Her article on the use of websites as an instructional tool was recently published in the TechEdge Magazine. In February 2011, her article, Lessons Learning In a 1:1 Classroom, was published by TechEdge. The article was republished in ISTE’s Learning and Leading magazine in August 2011. She was named Fairmont Junior High’s Teacher of the Year for the 2011-2012 school year. Carol is passionate about the positive impact that technology has on student achievement. Her presentations are packed with real-life solutions, quality resources, and humor. She has an ability to connect with her audience and motivate them to take technology integration to a higher quality level.
After checking out some of the problems, this looks a really good tool for encouraging group problem-solving, especially if it can connect students around the world. It’s too bad that it became so successful it had to be shut down. I sure wish I had the opportunity to use a tool like this when I was in school.
HI Kevin,
It’s exactly because of responses like yours that I want to restart it! 
Thanks for encouraging me!
Thank you! I’m working on a revival of MathWorld Interactive now!