On Mac, the plugin software (not the sound library) will be installed in these specific locations:

Macintosh HD/ Library/ Audio/ Plugins/ Components

Macintosh HD/ Library/ Audio/ Plugins/ VST

Macintosh HD/ Library/ Application Support/ Avid/ Audio/ Plug-Ins/

On Windows, the default installation path for the plugin software (.dll) is here:

C: Program Files Steinberg vstplugins - 64bit

C: Program Files (x86) Steinberg vstplugins - 32bit

C: Program Files Common Files Avid Audio Plug-Ins - AAX (for Pro Tools)

Note: On Windows, you have the option to install your plugin software (.dll) anywhere you would like. It's important that your DAW is looking in the file path where you install your plugin software, or your plugin will not appear in your DAW.

Each DAW has a plugin manager that allows you to select the file path where your plugin software (.dll) is installed. Please ensure that your DAW's plugin manager includes the file path that you chose to install your plugin software. 

Your standalone applications can be found in this location:

Mac:

Macintosh HD/ Applications

Windows:

C: ProgramData Spectrasonics

Note: To turn on Hidden Files and Folders in Windows 7 and later, go to Control Panel/ Appearance and Personalization/ Folder Options/ View Tab and select Show Hidden Files and Folders. Hit Apply.