ShareX is a Screen capture, file sharing and productivity tool. Nova is supported as a custom uploader. You can get ShareX here.
You can download a custom ShareX uploader profile which uses your nova account for uploading files on the account apps page.
Download the uploader config and choose 'Open file'

Set nova.storage as active uploader. Choose Yes

A simple tool for uploading files to
nova. Supports uploading to accounts, copying download
links to the clipboard and has an upload history screen.
An Android app for uploading and sharing files on nova. You can get a compiled APK package from the GitHub releases page.
go-pd is a command line interface and client library for nova created by Manuel Reschke. The CLI supports uploading files anonymously, and uploading to user accounts. The client library supports uploading, downloading and deleting files, creating and viewing lists and user accounts. Compiled binaries are available on the GitHub releases page.
go-nova is a command line interface for nova created by Junpei Kawamoto. You can use it to upload and download files and directories from your terminal. Compiled binaries are available on the GitHub releases page.
pdup is a little bash script for uploading files to nova from the terminal. It's available from GitHub.
If you know more open source apps which work with nova please send them to support@nova.storage.