Hi Muddypaws,
Plain old drying or fermenting depends on the plant.
Most seed is allowed to dry on the plant. Some seeds are in a gel that does not easily come off and fermentation removes the gel and also removes pathogens too.
So tomatoes seeds are fermented since they are in gel. You can smear the gel and seeds onto like a paper plate to dry and they will sprout late just fine. There is a few disadvantages to it. The gel keeps the tomato seed from drying as fast, the seeds are clumped together so separating them is a pain, and of course disease pathogens that might be tagging along with the seeds are not destroyed.
To fement, only a tad bit of water is added if needed, but normally the juice of the fruit is sufficient. Too much water actually hampers the fermentation.
Another seed that gets fermented is cucumber seed.
Pepper are not in gel so they would be removed from ripe fruit and left to dry on paper towels or plates.
Eggplants are also dry so they are not fermented. JUst an FYI about eggplant seed saving. Eggplants must be way over ripe to what we consider edible for the seed to be mature enough to harvest.
Hope that helps some,
Remy