One product that seems to be looked over quite often is Boris RED. The Boris family of products has a similar interface to after Effects, but I've always found it a lot easier to use, and a lot more powerful.

The website is at https://www.borisfx.com/ and, from there, you can download the 'keyframer', which is basically a fully-working version, but without the ability to render (you can save out, and render elsewhere, though...)