RetroUI is one of the many Start Menu replacements out there supposed to bring this traditional feature back on Windows 8, but it turns out that the app works quite flawlessly on 8.1 Preview too.
Even though it doesn’t provide support for this particular OS version, RetroUI installs and works just fine on Windows 8.1 Preview, without replacing the built-in Start button offered by Microsoft.
Instead, the app brings two different buttons on the Windows 8.1 Preview Taskbar, one of which launches the traditional Start Menu. Of course, it provides one-click access to the installed apps and to the built-in power options, just like the old version available in Windows 7.
The application is not available with a freeware license, but the available trial version gives you the option to try it out for a maximum of 7 days at no cost.
Update: a free version of RetroUI is also available. More information can be found here.