Sugar Rush (lost build of cancelled online game; late 2000s/2010s)
Sugar Rush (not to be confused with the fictional arcade game from the Disney movie Wreck-it Ralph) was a massively multiplayer online game developed by Klei Entertainment and planned to be published by Nexon. It was announced in 2008 when Min Kim, director of operations for Nexon, announced that a game was in development in Vancouver.
Testing for the game started in late 2008 and concluded that same year. During testing, players could choose between three different characters: a ninja, a brawler, or a morph. The main point of the game was to get as many coins as possible, and these coins were gained by battling other players. There were four minigames that could be played. The first one was Robot Battle, where players would fight robots that respawn. The difficulty could be adjusted to four different strengths. The details of the other three were never revealed.
Around July 2009, Nexon announced that they would not be the publishers of the game anymore, and as such, they would be closing the Sugar Rush website. Klei Entertainment stated that the game would still see the light of day, but it would not be published by Nexon. However, the game was announced to be cancelled in August 2010 by Klei.
A statement of the game taken from a blog reads:
Sugar Rush was built to be a free-to-play online arena combat game. Play with your friends or battle it out in a devious or lighthearted world. Sugar Rush showcased a stunning 2D visual that sets a new standard for free-to-play games, and features the artwork of Jeffrey Alaga, the longstanding director of Atomic Betty and other TV cartoons. Designed with Klei's quirky sense of design and polish, the game also featured a complete character customization engine. The game is out of print, but is fondly remembered by the staff of Klei." 
The game has not resurfaced since its original beta testing, but, since Klei Entertainment still exists and is still developing games, they still might have builds of the game, and maybe Nexon might have builds since that company is still in production as well.
The launcher for the beta still exists, but the servers have been long down, so the actual game is inaccessible.
- Min Kim announcing the then-unnamed game. Retrieved 10 Jan '19
- Kotaku article detailing some of the game. Retrieved 10 Jan '19
- MMOsite page detailing the Robot Battle minigame. Retrieved 10 Jan '19
- Blog post containing a description of the game and its cancellation. Retrieved 10 Jan '19
- Download link for the launcher (the game is inaccessible). Retrieved 13 Jan '19