AutoSizer

AutoSizer is a tiny tool designed to automatically maximize applications' windows. The application does not come with an interface, but you can access it from the System Tray. When you launch the tool, you are prompted to add the list of executable files in the newly created apps.txt file, so proceed to adding the applications you want to maximize here. In case you change your mind, you can always open the same page directly or via the Edit command (right click on it from System Tray) to make modifications.

On the other hand, take note that the tool does not come with extra functions, such as restoring the window or minimizing. You can get back the original application window by simply exiting the program and removing the executable from the plain text file mentioned earlier.

As you probably hinted, the program can come in handy for those older games and applications that do not have the maximizing feature. Generally speaking, with most applications you should be able to view the options somewhere in the upper menu. In case you don't, then pressing the Space bar while holding down the Alt key should bring this particular menu up and you can select the Maximize from here.