Tobor is the name of a scrapped texture that was found in the
props_training section of the GCF files, which were added as part of the Mac Update. It is unknown what the texture was planned to be used for, but it was speculated to be part of the Engineer Update as some form of Sentry Gun replacement or upgrade, as it shows what appears to be the tubes, eye, and metal casing of the Sentry Gun.
The texture of Tobor has been removed from the game's files as of the Engineer Update and is no longer found in
props_training. Its inclusion in
props_training suggests it was supposed to be used in a training map. The TF2 team has stated that tobor was a dump for a training mode that was intended to be playtested by a third party. They left the dump in the game, but it was removed.
- Tobor was originally created as part of a content dump. It wasn't supposed to ship into the game, as it served no purpose.
- Tobor is "Robot" spelled backwards, hinting at the texture being for some sort of robot used for training. 
- There was also an unused item quality called "tobor_a" in the game files. It was added in the June 11, 2012 Patch and removed in March 19, 2013 Patch.
- The word "Tobor" was referenced several times during the ARG leading up to the Mann vs. Machine update:
- In the map Foundry, a hidden room exists with a sign reading "Doctor Wilson's Auto-Borax Self Scrubbing Mechanical Soap". Two wooden planks propped up against the sign frame the letters to form "TO-BOR". Several other rooms in the map featured hints to the then-unreleased update.
- Near the end of the ARG leading to the update, an image was discovered on the TF2 website revealing a craft recipe for the Blood Brothers comic. Some of the letters on the recipe were visibly stained by blood; they were the letters in the word "TOBOR".
- The URL www.teamfortress.com/tobor automatically redirects to the Mann vs. Machine update page.
- Kayohgee, "Tobor's purpose, revealed!". . Retrieved June 6, 2011.