Pah! Seven string guitars? That's nothing. Introducing the José Ramirez 10-String Guitar.
And here's one from Woodfield Guitars which appears to have an extended fingerboard for the lower four strings. It looks way too complicated.
And if you think that's complicated, take a look at these 14 string guitars belonging to Paul Garthwaite and Michael Bianco, and No - these do not have the strings arranged in pairs (courses) as on a traditional 12 string guitar.
The prize for the most strings (albeit not all on one neck) must surely go to Pat Metheny's Pikasso guitar which sports two soundholes, three necks and forty-two strings in four groups. Unlike double-necked and other multi-necked instruments, this guitar is designed for compositions using all the strings played at once.