What is it for?
Hosted Mac Builder
The builder service allows you to develop iOS applications without a local Mac computer. All of the development steps can be done with the builder service including the final step which is uploading the application to Apple App Store. Note that the builder is currently limited to projects of up to 50mb.
If you are less experienced with Mac OS then it is recommended to start with the hosted builder even if you have access to a local Mac computer.
Oh! thank youI've removed the link. Looked a bit spammy.