Beep is a tiny command line utility for Windows computers that uses the internal PC speaker to make a notification sound. This can be useful in situations when you do not have a sound card or speakers are not connected or turned on. Freeware.
By default, a notification sounds is played, but you can use the program to create your own sounds with full control of what is played. Typical usage is in batch scripts or similar to signal events. For example, I use it myself to signal when my PC has booted and launched all startup applications and is ready to use.
Note: not all modern computers have an internal PC speaker. Some may use an integrated sound card instead. Some are just silent. Windows 7 seems to have removed this hardware feature all together for some unknown reason :-(