Arrowhead stated on their site that Gauntlet was going to come to SteamOS and Linux.

https://www.gamingonlinux.com/articles/gauntlet-action-rpg-from-warner-bros-arrowhead-to-launch-on-linux.3284

After over a year an official announcement on their Steam discussion board they stated the cancellation of the Linux version.

"Since all our focus has been needed on this free upgrade for PC, regretfully, the SteamOS version of the game has been cancelled." - http://archive.is/qXOQW

On the official page for WMDPortal they state the following...

"Project CARS 2 will be released for the PC, Sony’s Playstation 4, Microsoft’s Xbox One and Steam OS." - http://archive.is/31gBG

A trailer for Project CARS 2 was released and does not mention SteamOS or Linux.

- Reported on by GamingOnLinux[archive.is]

https://www.youtube.com/watch?v=kktEmHZ8M1A

On WMDPortal.com's page for Project Cars it states the following...

"Project CARS will be available for the PlayStation 4, Xbox One, Steam OS, PC, and Wii U starting Fall 2014." - http://archive.is/ABu8O#selection-391.0-391.107

After almost a year after thair initial expected release date they were asked via Twitter about the Linux version. They replied with "no plans" for Linux support.

http://archive.is/wvCrR

Odds are the person managing the Twitter account does not know that SteamOS is Linux, but when asked specifically there was no reply.

This is something I have been thinking about for a while.

On the one hand, it might be useful to know which developers make flagrent promises and to provide a track record.

On the other hand, they do finally deliver a Linux port so it's not entirely broken, only delayed.

What does everyone think: should BLP focus solely on if a title misses it's promised delivery date or mainly focus on if a Linux title never comes after being promised?

On Augest 27, 2015, the official Rocket League twitter account posted that the game will be coming to Mac and SteamOS within the year.

http://archive.is/OcIdQ

This was later changed to Q1 of 2016.

http://archive.is/5b1ti

Then changed to Q2 because dirkened misspoke.

http://archive.is/Tp1hj

As of this writing, it is Q3 of 2016.

Update: They finally released the Linux version.

Quick Update: Mac & Linux are set to be launched on the 29th! Multiplayer, localizations, and the version 1.1 update are still in process.

I am assuming July was ment since typically when a date is given without a month, the current month is implied.

http://archive.is/S8apA

Mark Rein of Epic Games made a reply on the official forums that "We like the PC. We like the 360. We like the PS3. We like the Macintosh. We like Linux. We will deliver UT3 for all of these platforms and it will rock on every one." in Augest of 2007.

http://archive.is/KjjmX

Ryan Gordon was the one who was tasked with porting UT3 to Linux. He even teased an image of it running on Linux and said "Seriously, there's no conspiracy."

http://archive.is/VBom

After being caught up in legal issues with a middleware provider, UT3 for Linux was never finished nor released.

http://archive.is/TMdkD

While the article implies that the issue was with Ageia Technologies because of the implementation of the PhsyX engine, there was no confirmation.

Capcom announced in a post on the official Steam page that Street Fighter 5 will be coming to SteamOS in the Spring of 2016.

http://archive.is/TqiRW

Spring has come and gone and not even an update in SteamDB.

http://archive.is/kGoX7

When asked about a Linux version, a developer said they are "still working on it" and is "actively being worked on".

This was in April of 2015.

Update - 2016-08-15:
Tripwire said on Twitter that Linux files will come post launch.

http://archive.is/IS4My

Update - 2016-11-21
Tripwire informed Liam of GamingOnLinux that they need a developer to continue with the Linux port.

http://archive.is/9tkRv

If nothing is announced by May 21, 2017 I will add this to the curator list.

UPDATE: GamingOnLinux reported that the Linux port of KF2 is being done by Knockout Games.

http://archive.is/U5GKX

The tweet that was quoted no longer exists, so we do not have confirmation. But, I trust GoL that it's accurate.

Originally posted by The Jesus:

Killing Floor 2!!!!!!!!

You are correct.

http://archive.is/kGoX7

And not only has it been over a year, there is nothing in SteamDB.