How to automatically update all Third party software in Windows?

You need a Package Manager like Chocolatey to install and upgrade all your software packages. Since it uses PowerShell commands, you can set a Scheduled Task in Windows to run monthly the upgrade command choco upgrade all -y.

Note that chocolatey only updates packages you installed via chocolatey itself, not the packages and softwares you installed yourself manually.

What you're looking for can be accomplished by a software manager. While there aren't yet any official managers for windows, there are plenty of third party options like Ninte. Their library is fairly small though, and generally only popular software is included. The only 3rd-party windows software managers that work with most software I know of are offered by chinese companies such as Qihoo 360 or Tencent, though I'm not entirely sure that even they still offer the software update and management portions of their product. You'll have to shop around a bit if you want to find one you like.

EDIT: I can now confirm that the software manager is still present on the products mentioned as of 2016-01-07, but only on the Chinese version.

There isn't a single application that I know of which can manage to keep all software on a Windows machine updated. However, FileHippo App Manager in conjunction with SUMo seem to take care of most of the updates.

Both programs require user intervention for installing updates although FileHippo App Manager can at least download the software updates automatically. SUMo seems to be only good at telling you what's outdated rather than fetching the update for you. My antivirus program also seems to think it's adware.

There's also Avast Software Updater but it only checks for and installs updates for certain software programs that may compromise system security if left outdated (e.g. web browsers, Java Runtime, Adobe Flash Player, etc.). However, it has the advantage of performing automatic updates without user intervention.