Currently I'm looking at GravCMS [1] as an alternative. It's free initially, but it can become somewhat expensive with many official plugins. But it's file format is Markdown, and one can combine multiple files into a so-called modular page. It has a backend for editing, forms and e-mailing of form submissions. Seems perfect for small and mid-sized company web site.
Another option I considered was Kirby [2]. Its backend UI is configurable. That's nice in theory but the documentation is somewhat lacking, in my opinion. I've used the starterpack and it took me hours to find the one command to be able to add new pages. Its content format is also custom, not Markdown. Finally, it's €100 per site.
Also, a few days ago, I stumbled upon Typemill [3] which I will check next week.