They’re ‘free-form’ frameworks based on the Stacks plugin. So instead of giving you a designed theme to work with, they let you create your own look and feel and give you loads of stacks elements to create menus, slideshows, columns, panels, contact forms, lightboxes, grids, galleries etc.
Foundation has been around for longer but both have their admirers and both are excellent if you prefer to have more control over how your website looks - rather than using a pre-designed template.
Whether one is more suited to what you want to achieve rather than the other is probably down to personal preference. Best way is to check out the many videos which showcase Foundation and Foundry and see which ‘chimes’ with you.