Online file manager?

I need a way to upload and download files to my server from anywhere. The perfect solution would be something php that would let me go to http://www.mydomain.com/files, then log in and get access to the files all in my webbrowser. I will need to have different user acounts som my co-workers can upload and see the files too. and it must be free, we cant afford something fancy yet, however i’m sure there are some sexy opensource stuff that will do the job. Something in the style of wordpress, mediawiki, phpbb etc.

Any suggestions?