I recently came across an interesting FOSS game (hat tip @ http://fossgames.blogspot.com/ ) that is presented really well through itch.io:
https://luckeyproductions.itch.io/hexon
(yes I noticed the 'NC' on the asset license, so FOSS is a bit debatable)
As you can see it is a really informative portal that also allows very easy collection of donations via the "name your own price" option.
Setting up such a game portal on itch.io is extremely easy (a matter of minutes with their website builder).
In addition they offer interesting developer tools as previously discussed here:
viewtopic.php?f=7&t=6690
And of course there is the open-source & cross platform itch.io client application (like Steam) that easily allows updating and installing of apps.
Yes, their server backend isn't open as far as I know, but as long as this is only one option to distribute your game, I think it is a really convenient and useful one.
Edit: I have no relation to itch.io, but I think they offer a great service and are the only ones with an open-source distribution client AFAIK.