THIS ARTICLE HAS BEEN SUPERSEDED BY How to type upside down.
I am not sure when it would be useful to be able to write upside down on a computer, but should you wish to do so, here’s how you do it:
Type your text into the uppermost box
Select the text in the bottom box and copy it to the clipboard (Ctrl C on a PC)
Paste the text into your document or web page.
This is what it looks like (based on the above text):
˙ǝƃɐd qǝʍ ɹo ʇuǝɯnɔop ɹnoʎ oʇuı ʇxǝʇ ǝɥʇ ǝʇsɐd ㄣ
(ɔd ɐ uo ɔ ןɹʇɔ) pɹɐoqdıןɔ ǝɥʇ oʇ ʇı ʎdoɔ puɐ xoq ɯoʇʇoq ǝɥʇ uı ʇxǝʇ ǝɥʇ ʇɔǝןǝs ᄐ
xoq ʇsoɯɹǝddn ǝɥʇ oʇuı ʇxǝʇ ɹnoʎ ǝdʎʇ ᄅ
/ʇǝu˙uʍopǝpısdnǝʇıɹʍ˙ʍʍʍ//:dʇʇɥ oʇ oƃ ⇂
:ʇı op noʎ ʍoɥ s’ǝɹǝɥ 'os op oʇ ɥsıʍ noʎ pןnoɥs ʇnq 'ɹǝʇndɯoɔ ɐ uo uʍop ǝpısdn ǝʇıɹʍ oʇ ǝןqɐ ǝq oʇ ןnɟǝsn ǝq pןnoʍ ʇı uǝɥʍ ǝɹns ʇou ɯɐ ı
Some uses for this facility could be:
Special effects in a story.
Yes, you could simply enter the text in the usual way, and then turn the page upside down, but that doesn't allow you to mix normal and upside-down text in the same document.
An alternative might be to create a document in the normal manner, and then scan it into the computer as an image, which you can then insert upside-down into an ordinary document. However, not only is that a whole ton of hassle, the quality of the text in the picture will almost certainly not be as clear as the ordinary text.
So, it looks like for producing upside-down text on a computer, that upside-down website is your best bet.