Is there any app really simple to compress videos on Mac?
Something like JPEGmini for videos (do not resize, just reduce file size).
I just know Handbrake, but it is not the most simple solution.
It is not free, but Apple itself has an app called Compressor.
You can see its information here: Compressor
Usually it is used together with Final Cut Pro, but can as well be used standalone.
I quite like MPEG Streamclip. I use it quite often and while it offers most of the options of HandBreak (and some it doesn't), it can be a drag-and drop video compressor if your want.
I like Macroplant's Adapter. It has a list of presets and is really easy to use.