Thanks for the infos. wwwoffle looks promising.
Proxy offline browser is another alternative, unfortunately it's proprietary software, and the saved pages only look good if you view them through the proxy. If you open the html files directly in the browser, the images, css, etc. are not displayed. And proxy offline browser only keeps the latest version of a page.
If someone wants to store several versions of a page, you might want to search for a "warc proxy" on github. Such a proxy saves your browser traffic into warc files, which let's you later create your own little wayback machine with the help of the openwayback software. However I tried some of these warc proxies a few years ago, and they all seemed pretty unstable or just didn't work at all, but maybe I just wasn't using them right.