What it says on the tin.
I use Streamtome. Works well, and I have yet to find an unsupported format, other than DRM content.
I love Plex, but if all you’re wanting to do is stream a few movies on your PC it might be overkill. On the other hand, it’s a really wonderful and mature product with a huge user base.
Since this is a software question, moved to IMHO (from Cafe Society).