At this time Showit doesn't have any client gallery functionality built into the platform. You can create +sites to display your clients images beautifully if you so wish, but it is for just display and wouldn't be a solution for delivering images to clients.
Link to an External Client Gallery
While Showit doesn't have any options for direct integration in the platform with third party client galleries like those listed above, you can link out to those +site galleries. You can use our URL click action to link directly to your +site client galleries from your Showit site.
Here is another great option: CloudSpot Galleries + Showit