Keys3 is a proof of concept s3 browser client written in kotlin with server side templating courtesy of Kweb
A live demo is running here: http://brows3r.shiveenp.com
The cool thing about Keys3 is that unlike other apps it's meant to be entirely server side rendered with only the initial page sent at startup. Once started the user can interact with the application and get the data for their S3 bucket by filling up the requested fields.