MountUp is one of the roughly one billion mounting mods that exist today. What makes this different from all the others is that it does one thing and one thing only: it gets you to mount the best mount for your current location. It is based on the LibMounts library, which does all the heavy lifting of picking the correct mount type for your location.
To configure the mod, put the global macro named "MountUp" on your bar, and type /mountup.
Determines if an air, land, water, Vashj'ir, or Ahn'Qiraj mount would be the best mount to use.
Allows you to exclude certain mounts from being used.
Picks a semi-random (see "Will not be implemented" below!) mount from the mounts that you've chosen to use and updates a macro to use that mount.
Worgen players have "Running Wild" as a land mount option.
Druids have either "Swift Flight Form" or "Flight Form" as an air mount option, and "Aquatic Form" as a water mount option. Also, druids with points in the "Feral Swiftness" talent will use Cat Form while indoors.
Shamans with points in the "Ancestral Swiftness" talent will use Ghost Wolf while indoors.
Druids and/or Worgens that are leveling may not have abilities picked up as they are learned. Worst case scenario, a /reloadui would be required after training your mounting abilities (Running Wild/Flight Form/etc).
Race/faction changing from a Worgen to something else will likely result in Running Wild sticking around as a land mount option. This will likely be fixed in a future update.
Will not be implemented:
Random mounting. When the location's mount type changes (going from a non flyable area to a flyable area, for example), a random mount is chosen. However, this is not the same as your typical "pick a different mount every time I mount up" option.