Dropbox - Online Sync and File Sharing
Tabbles - Tabbles use tags to organize and find files along with your colleagues.
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
TagSpaces - TagSpaces is an open source platform for personal data management. With TagSpaces you can manage and organize the files on your laptop, tablet or smart phone.
Google Drive - Access and sync your files anywhere
Elyse - The free version allows up to 30 tags.