This isn't really a module. In Linux a module is something you load into the kernel or into an application to extend their capabilities.

The X client that displays a user list for login purposes is called a "display manager."

Yes. Most web cams are supported by the v4l (Video for Linux) module.

modprobe module_name inserts a module
rmmod module_name removes a module

The NTFS file system is supported in Linux by both a kernel module and several userspace programs. It is not supported as a root file system and is not recommended for permanent file storage.

Most screensavers on Linux are modules run by Xscreensaver:

http://en.wikipedia.org/wiki/XScreenSaver

I don't know exactly how to convert a program to a module, check the Xscreensaver documentation.