This is a reissue of C-chan's logo for the OS-tan Collections Wiki, featuring Mac OSX Server-tan (aka, "Rhapsody") and Windows NT-tan, as well as their two immediate daughters Darwin-tan and Inu-T (aka, Windows NT 4.0-tan). Aside from the enlarged size and the removal of the "OS-tan Collections Wiki" logo (so you can insert whatever you'd like in the treasure box), the image is left completely in its original entirety.
Though initially added to the logo due to a contest, both OS-tans are mothers of the modern Mac OSX and Windows line so in the end it seemed fitting that the two would represent an information repository for all of the OS-tans. Darwn and Inu-T were added [and left unfinished] after the fact, to add a little comic humor with their,... "food fight".

I do recall that this version of NT-tan garnered a lot of complaints about her chest-size. As if that could have been prevented, given that no two NT-tan pictures from Futaba ever showed her the same way. ^^'
And she is quite flat looking here-- good thing I usually take notice of other anatomical details first. Like collarbones!