The rachatdecredit theme is almost certainly a custom theme, you can tell from the URL for the stylesheet. Most of the time if a theme is in a directory with the same name as the site it is custom, or at least a child theme:
http://www.rachatdecredit.net/wp-content/themes/rachatdecredit/style.css
Since you want something very basic, I would suggest you build a custom theme or a child theme of the standard Twenty Theme. WordPress is great for theming because it mostly gets out of the way and lets you do what you want. Much of the complexity of a theme is handling the blogging aspects, so since you don’t want those a custom theme should be pretty simple.
Since you want simple you might do more work to get an existing theme to work for you than to build it from scratch.
Here’s a link to an answer I wrote about how to write your own theme:
And here’s one about creating a child theme:
The child theme approach might be easier since you’ll be able to start with a working theme and incrementally modify it until you get what you want.
If those are not options for you and you really want to use an “off-the-shelf” theme then there are hundreds to choose from. And that’s the problem; which one? I could start researching them to find them but I don’t know what you’ll like so it might be better to just start doing the research on your own. I also don’t know if you’ll consider commercial themes or only want free.
If you must find an off the shelf theme, by googling “wordpress themes” or going here: