T-Chip, which is short for TimeChip, is a program written by Ruben Spaans. It modifies the original level set to change untimed levels to a 999 time limit and creates a new executable called TCHIP.exe. Scores achieved with this are not legal for official scorekeeping purposes, but they are counted as a separate competition alongside, with the theoretical bold score if there was a 999 time limit being the goal. In the 29 untimed levels in CC1 and three in CCLP3 - as well as any notable custom levels with no time limit - this wiki states the unofficial bolds to those levels.
Nowadays, level editors can do the job of T-Chip manually, and Tile World keeps track of T-Chip times on untimed levels just as it would a time on a regular level, so T-Chip is generally not used today.