The TSUKI (月) Project was a website based on the belief that our reality is just one system among many in the universe, and that when we die, we ascend to the next system.
Several references to the anime TV series Serial Experiments Lain were present on the website and its multi-reality theories.
In January 2017 a 4chan user, named Tsuki, get attention by launching the TSUKI Project. 
The TSUKI Project alleged that by joining the website, the users called migrants, limited 15,000, would ascend from the SystemSpace (our present system) to the next system once they die, but it warned users to not commit suicide.
The website gained interest from the internet community after being featured in numerous YouTube videos. Several theories were born from it as some said it was a hoax, others a death cult or even a marketing stunt for the release of a new game/tv series. Most information on the website was purposely cryptic with links leading to images of static and black and white pixels, leading even more theories about encrypted message hidden on the website.
The site had a countdown that ended in early 2017 but it was for announcing a new website called ARISUCHAN which was a Serial Experiments Lain fan-oriented website. The TSUKI Project website was since then taken down.
Serial Experiments Lain
Many theories from users about the TSUKI Project made link with the anime tv series Serial Experiments Lain. In fact, the website itself made it clear by having the protagonist on its banner. The story about Lain discovering a virtual world where you can upload your mind since a direct inspiration for the TSUKI project.
Lain herself became the mascot of the website and gained great affections from the users. As the website worked as a forum around the TSUKI Project, it was a prevalent place for sharing Serial Experiments Lain pictures. Because of that, most subscribers used the website as a fansite for the tv series without believing in the SystemSpace theory.
The new website ARISUCHAN made even more connection to the series. The name is a direct reference to one of the series protagonist, Alice and their banner is a picture of Alice and Lain together. ARISUCHAN was not considered like a new version of the TSUKI Project but the result of an internal conflict about the TSUKI Project website and the desire to dissociate the project and the Serial Experiments Lain content.
- TSUKI Project website (archived)
- TSUKI Project website (mirror)
- The TSUKI Project explained (reddit)