The 968 is so closely related to the 944 that Porsche originally planned for it to just be a variant of that car, but so many components had been modified that they figured it would be easier on the buyer if they just gave it a new model name.
There was only one engine sold with the 968. It was a 3.0 liter I4. It was the most powerful non-aspirated 4 cylinder engine ever made by Porsche or any other car manufacturer. This engine was paired with either a 6 speed manual transmission or a 4 speed tiptronic, which acted like an automatic but had a steering wheel option to switch over into a manual mode for a few seconds.
These cars were only sold as a 2 door coupe or a 2 door convertible.
The 968 Club Sport was the performance version of this car. It was stripped of some features to decrease weight and some performance features were added.
Total production of the Porsche 968 was about 12750 worldwide, but in the United States only about 4600 were sold. The Cabriolet and coupe numbers are split about 50/50. If you would like to buy one, check the current pricing by looking at the listings on eBay. You might just want to buy from there. You can also find some parts if you need something to fix one up.