A simple workflow that does a few things with downloaded files:
Install the last downloaded file
Open the last downloaded file
Install a specific downloaded file
Open a specific downloaded file
The workflow will automatically mount DMGs and move the enclosed .app file to /Applications. If the DMG includes a .pkg file, it will be opened.
Latest version: https://github.com/cmer/alfred-opendl/raw/master/Open or Install Last Download.alfredworkflow