Add upload and download of files to our website (PHP)

Hello, We currently have a school management website. We need an area in the admin view where we can upload and download files. We need a way of seeing all the files and folders, as well as deleting the files, moving between folders, etc. If there is any open source PHP file/folder structure management tool, then we are open to using this. Additionally, we need a special feature when files are downloaded : check-in/check-out. How this works is this - when you download a file, you mark on the file, and the file is set as "checked-out" with your name beside it. Others can download the file, but they are warned that the file is checked out. A checked out file cannot be uploaded by another user, only by the user who checked it out. When the user who checked it out uploads it again, then this file is marked as checked-in and another user can then download and upload it. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform Firefox, IE6, PHP