As a few others have mentioned, Corruption Time had a really promising start and is usually the first game I think of that I wish had continued.
Surviving With My Daughter was another one, only had one release that had a lot of hype around it and then something happened soon after caused the dev to disappear and that was that.
Obscure Affairs also comes to mind. Even after the changes to some of the characters, I was still pretty interested in seeing it continue, but it looks like that's not happening now.