Thinking with Time Machine is a 2014 modification for Portal 2 developed by Ruslan "Stridemann" Rybka and published by SignHead Studio.

[3][4] Looking down at the tablet allows the player to record and control their movement, including walking, jumping, and picking up objects.

[3][7] The campaign starts at the end of Portal 2, after which the player is introduced to the time machine concept through a series of tutorials.

[9] Thinking with Time Machine was developed by Ruslan "Stridemann" Rybka and published by SignHead Studio.

[9][6] The mod was released on Steam for free on April 18, 2014, for Microsoft Windows, OS X, and Linux platforms.

[7] Christopher Livingston of PC Gamer also praised the mod, saying that "it's very cool watching the past version of Chell appear and run through her recording".

[3][12] Livingston and Sergey Svetlichny of ITC.ua compared the time machine concept to functions of the cooperative mode.

[3][6] Phil Savage of PC Gamer also praised the time machine concept and stated that the mod "dramatically expand[s] the complexity" of the Portal series.

[16] Reviewers have noted that the game lacks usage of the portal gun; Livingston and Moore saw this as a net negative.