I am loving all of the games in the Solarus engine. 
I am playing these games in Retropie and they have quickly become my go to games when I have the time. 
 
My biggest problem is trying to play "In Development" games.  They don't provide a .solarus file and I haven't been able to get any of the .zip files to play. 

Any help is appreciated.

I figured it out.  So, for other Retropie users, download the file and rename the data file with the .solarus extension.