sokolov22: 3) While the GOG page does not mention Cross Platform Multiplayer (I am not even sure if GOG has such a tag), the Steam page does (
http://store.steampowered.com/app/290340/), and the devs said in their reddit, livestreams, etc. as having Cross Platform Multiplayer support
Just a comment on the Cross Platform Multiplayer tag.
1) When Steam mentions Cross Platform, they usually mean Windows/Mac/Linux as platforms. Whether you count those as different platforms or different OSes is none of Steam's concern.
2) GOG uses the term Cross-play instead of Cross Platform Multiplayer, as can be seen on the
AvP gamecard (you may need to expand the description to see it). Not sure if all GOG games that support Cross-play have that notice though.
3) There is also the case of 2007's [url=https://en.wikipedia.org/wiki/Shadowrun_(2007_video_game)]Shadowrun[/url] which allowed Windows and XBox 360 players to multiplay together. That would be a third case of Cross Platform Multiplayer, different from the above two.
Pre-post edit: I see you already got your refund, though it may have been possible to contact Armello's publisher, explain the situation, provide a copy of the receipt and ask them for a steam key. Not sure that they would give one, but most Indie publishers are reasonable people.