Are there anime named after a manga, but totally different from it? Lots of manga get an anime adaption, and pretty often the anime's story deviates partly or a lot from the story told in the manga. This usually leads to different endings lacking information, or even giving surplus information as compared to the manga with the same name.

But this also made me wonder: is there also an anime that shares the same name as a manga (it supposedly was based on) but deviates 100% from this the story as told in the manga? So the story in the anime is totally different from the manga, but still shares the same name.
Sorry, this is not manga, but I'd like to mention The Idolmaster.

The original game of The Idolmaster is an arcade game about producing girls as idols.

However, the first anime series Idolmaster: Xenoglossia is a robot anime.
Girls ride big robots named "IDOL".

EDIT: Added some background of my understanding.

Mushi Production

Mushi Production 
is one of first animation studios in Japan.
Mushi Production is known for Tetsuwan Atom which is the first Japanese anime series.
Mushi Production was founded by Osamu Tezuka who is "Godfather of Anime" and the Japanese equivalent to Walt Disney.
This studio was created by manga/anime creators (animators).

At Mushi Production, animator's opinion was most important and business-side people didn't have a voice.

Lacking business sense, Mushi Production bankrupted in 70's.

Sunrise

Sunrise is a spin-off company from Mushi Production.
The founders of Sunrise knew why Mushi Production failed, so they decided a new policy that have strong business executive members and animators can't poke to the business side.
For example, animators can't become board members of Sunrise.
At Sunrise, it moves in the opposite way: animator's opinion is NOT adopted.

Sunrise had a big success in robot anime.
For example: Gundam, 
Code Geass 
and My-HiME.

Namco

In 2007, Namco (the game company that created Idolmaster) finished acquiring Sunrise and merged executive members.
In that time, Idolmaster was one of the most successful games by Namco.
The executives gave an order to the animator team that created My-HiME to create an anime version of Idolmaster.
Animators at Sunrise were professionals of robot anime, they weren't fit to make idol anime, but they had a policy. Therefore, they created robot anime that used characters of Idolmaster.