MapStory's website is a "compliment" to Wikipedia, according to the MapStory website. Ultimately, its goal is "to enable any student, teacher or practitioner on Earth to tap the power of this new mode of conveying one’s stories, arrayed across geography and as they unfold over time. " Sounds like a great open source GIS goal!
Let's take a closer look at how it is trying to achieve this noble goal. First, the site uses open source software called GeoNode. Second, MapStory is well organized into discrete sections. So, if you are only interested in certain topics you do not need to look at every map. Thirdly, you need to get invited to publish your MapStory. That's right, this is not a free for fall! See the "How To" tab for the simple step(s). Lastly, the site has a nice social feel, and you can search by Storyteller.
Note: MapStory although similar in name is different from ESRI's Story Maps site.