Thank you for your interest in HyperCard Online. Unfortunately due to a issue with our web hosting provider, the online uploader is currently not available. We hope to be back soon! In the meantime, why not check out the large collection of HyperCard stacks that have already been uploaded - there's over 3,000 now.
If you have a stack you want to upload, you are more than welcome to email us or reach out to us on Twitter. As always, comments, feedback and suggestions are most welcome.