Hi there.
Look out for the "Get it" button, instead of the misleading "Download" button which is part of a badly placed advertisement.
There is no need to pay anything here for a download, however not all games are downloadable.
The FAQ might answer your questions:
http://www.abandonia.com/en/faq
Please also see the following thread about this topic:
http://www.abandonia.com/vbullet/showthread.php?t=29786
Hope that helps.