PopIt will let you enter and access data easily from your code. It will also let you upload existing data to quickly populate a new site.
The API will let you access and modify all the data in PopIt, as well as storing your own custom data. Please see the API docs for more details.
We use the API from the editing interface on the website to be sure that all interactions with PopIt can be achieved through the API. It is not an afterthought - it is a core piece of the site.