The more recent instant dry yeast is intrinsically the same as fresh yeast, except that the yeast has been further dehydrated and encapsulated in a layer of dead yeast cells and some growth medium, which allows the living, encapsulated cells to remain viable. These are generally vacuum packed to remove any air. The resulting effect is viable yeast with a much extended shelf life but with fewer viable cells than fresh yeast. Instant dry yeast usually contains an emulsifying agent such as sorbitan monostearate, which allows it to mix easily in the dough.
We also find specialized forms of yeast, like osmotolerant yeast, which tolerates high percentages of sugar in the dough.
Another type of specialty yeast is rapid-rise yeast that provides an increased fermentation rate. There are other specialty yeasts such as yeast used for frozen dough, etc.