Aptoide Downloader lets Linux users download .apk files directly on their computer from Aptoide.com site. Phone versions requires Busybox and a terminal emulator. Tested only on Galaxy S2.
Run the script with either an Aptoide-URL or the package name of the desired app:
aptoide https://messenger.en.aptoide.com/app aptoide com.facebook.orca
To find the Aptoide-URL, go to https://aptoide.com/, go to the page of the desired app and copy the URL from the URL-bar.
PS: A big thanks to the guys that improved this script.