The TI-99/4 home computer line was produced by Texas Instrument from 1979 to 1984. It is comprised of just two models. The original 99/4 was a commercial failure, as it was overpriced and had a terrible "chiclet" keyboard. It was replaced by the 99/4A, which offered a better keyboard, much lower cost, and more expansion options. And for a brief period, this was among the most popular computers in the American market.
However, TI made two fatal mistakes. First, they entered a price war against the VIC-20, and they couldn't out-cheap Commodore. Even though this helped increase their market share, matching prices with a machine that was much cheaper to produce meant it ultimately had to be sold at a loss. Second, they tried to follow the "razor and blades" business model: while other machines included full documentation and schematics, TI was very secretive and disincentivized third-party development, wanting to be the sole provider of applications and add-ons for their own machine. This led to a very limited software library, which dampened interest in the system.
TI then discontinued the 99/4A, but remained in the computer business producing far more lucrative IBM-compatible PCs.
Note: software-wise, the two machines are fully compatible with each other, except for a very small number of programs (such as Parsec) that used the "graphics 2" mode, and consequently were only compatible with the 4A. Also, the later 4A units (which boot to the message "©1983 TEXAS INSTRUMENTS V2.2") use a lockout chip to not run unlicensed third-party cartridges.
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