Powders available: Real black powder from Goex, Swiss, or any number of other manufacturers, (Goex being the most known, if not the most common in the states anyhow)
These are available in a number of granulations from 1f, (cannon) to 4f, (priming flintlocks).
Also available are a number of substitutes, (Pyrodex and Triple 7 being the most common)which are widely NOT recommended for various reasons. IMHO some of these reasons are valid most not so valid.
Uses: Traditionally, 1f is used for cannon; 2f for larger bore (.45 cal and above) rifle and smooth-bore / shotgun; 3f for smaller bore rifles and pistols; and 4f for priming the flash-pan of a flintlock.
Actual use varies from shooter to shooter, most that I have had the privilege of knowing find 3f to be a good balance for all general BP shooting including shotgunning. Some even prime the flash pan with it.
Hope I didn't bore you with the basics, but your question was what is available and what is its uses are..