If you're looking for manga similar to OSTER project: Decaf Girl, you might like these titles.
Hachune Miku is the small and spirited spin-off character of the famous Hatsune Miku. Equally recognizable by her long pigtails and affiliation with leeks, Hachune Miku and her friends go on their own adventures.
This is the (imaginary) beginning story of the crazy popular Vocaloid Character GUMI!! By some freak incident, the now cyborg school girl has her eyes set on her idol debut as "Gumi" under the mysterious organization, "Intane Group"!?
An official gag comic for the TV anime, "KIZNAIVER" appears! In this gag comic, all of the "KIZNAIVER" characters have turned mini, and live out unbelievable days in Sugomori City. You get to enjoy a slightly different story from the original.