Windows/Linux: Whether you want to produce an amateur news segment, deliver a teleprompted speech, or just record a video message without a lot of "ums", free, open-source application TeleKast is a solid desktop teleprompter worth checking out.
Over at cool-stuff blog Cool Tools, former TV commercial director and producer Jeff Bragg gives TeleKast a runthrough in the video below:
TeleKast if a free download for Windows and Linux only. It's currently an alpha release, so you might expect a little bugginess — but it worked like a charm in my tests. If you'd prefer a little teleprompter action without installing an application, check out previously mentioned CuePrompter.