Connection: Madoka Magica Illustration Book is a project led by Purinpurin (プリンプリン) that includes illustrations from eight different artists. And all of that sounds good in theory, but there's only one illustration by each artist, making it a rather short collection ^^ But, it was released for the one day event Magi Madoka ONLY - Mou Nanimo Kowaku Nai (魔まマ オンリーイベント～もう何も恐くない～) so there wasn't a lot of turn around time.
I have an inkling Haruse Hiroki came up with the title Life of Negentropy considering the previous, interestingly titled Mimesis, from the last Comiket. Life of Negentropy is a Comiket 80 release by Haruse Hiroki and Tiv features art from Puella Magi Madoka Magica, and actually includes several notable guest artists in the collection.
For the one day event Magi Madoka ONLY - Mou Nanimo Kowaku Nai (魔まマ オンリーイベント～もう何も恐くない～), Nao Shirahane (DMYO) of Snow Ring teamed up with Nishimata Aoi from JOKER RING to create a most awesome Madoka doujinshi, Puella Magi Madoka Magica CONNECT. The doujinshi was part of a set that included a bag along with a clearfile that featured a joint illustration by the two artists with Kaname Madoka and Akemi Homura.
While looking for Puella Magi Madoka Magica illustration doujinshi, I encountered several new artists along with an event titled Magi Madoka ONLY - Mou Nanimo Kowaku Nai (魔まマ オンリーイベント～もう何も恐くない～) that ran for just one day on April 24, and was strictly Madoka doujins only. Jem & Lights Puella Magi Madoka Magica Fanbook by Sugi (スギ) was one of the many releases, and it presents a full color collection of Madoka art.