Ebiten: Kouritsu Ebisugawa Koukou Tenmonbu

First, the most obvious, the art. Same artist. Then I just watched the first episode and like Seitokai no Ichizon, they didn't do anything but to mess around in their club room. 

similar comedy, lots of random parodies, same animation, weird plot twists at the end that suddenly make it a serious show, and 2 Seitokai no Ichizon characters show up at the last episode as cameos 

This anime is quite funny both have refferences to another anime Has some ecchi moments 

•both have the same character art style •both animes are of the school/comedy/parody genre •both anime are focused on a group of students in a club •both are a harem where the boy is situated in nonsensical moments •both have references to many other animes that make the anime more interesting •they are really similar in the comedic/character design way, if you enjoyed one you would enjoy the other. 

Both are about an astronomy club, but while Ebiten's staff is only composed by female members, in Sora no Manimani there are also male characters. Also, as an anime Ebiten is a little more stereotyped then Sora no Manimani. 

Same club that is about astronomy 

One boy, many girls doing nothing at school club, and Shion/Chizuru-like character Anyway, I found GJ-bu similar Ichizon, and Ebiten similar GJ-bu and Ichizon too