Azumanga Donjara Daioh had a prototype version of it, screenshots showing the prototype was distrubted to magazine companies to advertise the game. Earliest screenshot was shown on February 22nd 2002 in Famitsu magazine.
There are plenty of small differences between the released vs the prototype version of Donjara Daioh. The prototype version has no shadows for any of the Donjara Pieces instead of there being a shadow. It has a black border around the character icon instead of no border. The "あ!" donjara cursor is positioned higher than the released one. The "1" is colored black instead of red. The recently used donjara pieces icon on top doesnt have the white border in the prototype version compared to the released one. It appears the animation with Sakaki and the cat running across the Donjara pieces has different timing between the Prototype and the released one. During this Animation, Sakaki has a shocked expression, the expression shown in both versions are different, and the prototype expression is not in the final version.
The websites tsutaya and bandaigames, and even the Donjara Daioh Manual, all use Prototype screenshots depsite the game having been released.
In the character selection screen, theres is quite a bit of changes between the prototype and released versions. The story logo in the prototype version shows a "ス!" instead of "ストーリー". The Donjara icons don't have a background behind them and the characters are cropped differently. The "?" for the unlockable characters is a simple black "?" instead of the white "?" with purplish/blueish scribble of color behind it. The prototype background contains colors of yellow, green, purple, blue, and gray, with all 12 characters vs the released background which has greens and yellows in the background with the 6 starter characters. The "あ!" selection icon is blue instead of orange.
The background in the prototype version contains all of the unlockable characters, which in the released version, this background is nowhere to be seen even after unlocking all characters. I believe this change was to make it more of a suprise when you unlock a character than to be shown which characters you can unlock beforehand, but that's just my guess.