Projection Distance Calculator will determine image size or projection distance.

NCH offers many free programs for creating, editing, converting & streaming video, audio, and graphics. This site is a GOLD MINE! Windows, Mac & Linux.

Google is another source of great, free applications.

Gimp has many powerful PhotoShop-like image-editor features.
Gimp for Windows -- Gimp for Macintosh -- Gimp for Linux

If you want basic photo editing with a simpler tool, try:
Picasa for Windows, or Kodak EasyShare for Win/Mac/Unix.

Audacity is a good audio editor which can open and convert: wav, mp3 & aiff (but not wma). Windows, Mac, & Linux.

VideoSpin video editor: edit, add transitions, titles, audio & sound effects, save as a file, upload to YouTube, etc. It even imports .mod files from camcorders with harddrives (which MovieMaker does not). Windows only (Macs use iMovie).

Try DVDStyler to author a dvd in Windows. Windows only (Macs use iDVD).
This DVDStyler QuickStart Guide might help.

VLC will play many formats of video and audio, including PAL dvd's with region codes. It can even grab a still-frame from the video. Windows, Mac & Linux.

Video Download Helper installs into the FireFox web browser, downloads video (including Flash/YouTube), and converts it to almost any format. Specify what you want in the Conversion section of Preferences.

Skype is a desktop audio and videoconferencing tool. Can do multi-person audio, but only 1-to-1 video call. Requires installation of software. Windows, Mac, & Linux.

TokBox is desktop videoconferencing which allows multiple users and integrates with Facebook. Runs in a web browser, so nothing more to install. Windows, Mac, & Linux.

V-Room desktop webconferencing includes video, audio, text chat, shared whiteboard,application sharing, and more for up to 3 computers at once. Runs in a web browser, so nothing more to install. Windows, Mac, & Linux.

Yuugoo is desktop webconferencing which allows screen sharing and remote control of another computer. Free for up to 5 people; $15 per month for 30. Requires installation of software for leader but not for viewers. Windows, Mac, & Linux.

Dimdim desktop webconferencing is free for 20 people. It allows sharing screens, documents, whiteboard, and will record the conference. Win, Mac & Linux.

Find lots of clips and complete tv programs & movies:
TV Land
Hulu
YouTube
wwiTV provides over 2500 international tv channels.
LIVE365 lists many internet radio stations.

Setup and operate your own internet tv channel with Mogulus.

Send & receive large files (1GB) with TransferBigFiles.com.

Modify Acrobat PDF documents with PDFTK Builder. It will re-order, delete, & duplicate pages from a pdf file, split a pdf, combine multiple pdf's into a single one, add a watermark, rotate pages, and even password-protect it from further changes. Windows only.

Use Response-o-matic to create user response forms.

Use SurveyMonkey to create & administer online surveys.

Need Clickers? Collect real-time audience responses from their cell phones with Poll Everywhere. Free for up to 30 responders.

CreateSpace is a company which will publish and distribute your original book, Audio-CD, or DVD, then send you a royalty.

Create your own games!
If you don't know which program to use, try Panda3D (Win/Mac/Linux) or EasyWay Game Engine (Win/Mac/Linux).