Quoted from a blog by Sander Berkouwer
Add or remove programs
Again there are two ways to get information on the software that is installed onto your Server Core installation in absence of the “Add or Remove programs” Control Panel applet. (also known as appwiz.cpl)
Registry
The first way is by checking the registry keys underneath the following key:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall
Luckily Server Core offers regedit.exe and regedt32.exe to digg deep into the registry of our Server Core box. Actually the “Add or Remove programs” Control Panel applet checks these registry keys at well. Since we all know how long it takes to get a complete list of all the software on your windows box it’s obvious this method takes a lot of time.
As this TechNet page points out the software packages that are listed underneath the Uninstall registry key all have a registry value associated with the UninstallString. You can use this value as a command to uninstall the software.
WMI
The things that are better left unspoken : Add or Remove programs in Server Core