Opera

This is a silent installer and uninstaller for Opera.

<package id="opera" name="Opera (WWW browser)" revision="1" priority="0" reboot="false">
 <check type="uninstall" condition="exists" path="Opera" />
 <install cmd='%SOFTWARE%\opera\ow32enen802.exe /s' />
 <remove cmd="%PROGRAMFILES%\Opera\UnInst\UNWISE.EXE %PROGRAMFILES%\Opera\UnInst\Install.log" />
</package>

On Opera 9.x /s seems to bee not enough. You had to add /v/qn Upgrade from Opera 8.x worked well.

<package id="opera" name="Opera 9.02" revision="902" reboot="false" priority="1">
 <check type="file" condition="versionequalto" path="%PROGRAMFILES%\Opera\Opera.exe" value="9.2.8585.0"  />
 <install cmd='"%SOFTWARE%\opera\Opera_9.02_Eng_Setup.exe" /S /v/qn' />
 <upgrade cmd='"%SOFTWARE%\opera\Opera_9.02_Eng_Setup.exe" /S /v/qn' />
 <remove cmd='"%PROGRAMFILES%\opera\uninst\opUninst.exe %PROGRAMFILES%\opera\uninst\install.log' />
</package>

You can also unpack the installer (i.e. with 7-Zip) and install the MSI directly.

msiexec /qn /i "%WPKG_INSTALLERS%\opera\Opera installer.msi" INSTALLDIR=%ProgramFiles%\Opera9