I launched Filestash [1] as my response to the infamous “Dropbox should just be FTP” comment. Once I had a decent FTP experience, I kept going: adding support for pretty much every storage protocol, plugins to expose Dropbox (or anything else) over FTP, SFTP, MCP, or S3, and all the features I wished Dropbox had, with plugins to customize everything.
The base product is open-source and I make money from custom builds, additional plugins, paid support, and the occasional extra feature for companies with specific needs. It's a bit more than noodle profitable but quite under a normal salary.