Sorry, but there are no free plugins for AE 10.5 that I know of. However, there are free tryout versions of almost every plugin available. They let you learn how to use them.
You can't make good-looking video with them because they put a colored mark or a watermark on the picture. When you buy them, you can use them for real.
There are some free plug-ins. See the last section on this page for links that will point you in the right direction:
But know that this actually isn't very useful as a broad question and answer. What are you trying to accomplish that you think that you need more plug-ins for? Answering that will help us to help you.