I have a big php/ajax web app and I need to assign tasks for coders to work on this application. I don't want to have to give them the full source code, db, etc. Is there a FTP tool that coders can use to work directly on my web server, and have it be similar to working on their local machine? (assuming web connection is fast, etc.) thanks.
Yes, It's called nautilus, the file manager in Gnome. It lets you browse and edit files as if they were on the local filesystem. I think you can do basically the same thing in IE. Or you can use and IDE like Aptana or Netbeans that supports synchronization that allows them to work on the files they need and will sync them when they are changed.
Give a try to Subversion which is a free source code version control tool with lots of options. If you are willing to buy a product you may have a look at SourceGear Vault.