Trying to picture what would look nice to me. Could be just what you would hate. Juniperus conferta 'Silver Mist', Blue rug juniper, Juniperus 'Pancake',Blue dunegrass (Leimus?), the yucca that blooms at about 3 feet in height,Amelanchier stolonifera, really dwarf mugho pine, Juniperus'blue forest',Rhus aromatica 'gro-lo', Daylily, Hen and chicks and sedums,Comptonia peregrina and low growing forms of Ilex glabra and bayberry, if you can find them.

Thanks for the feedback. We have to drive cars over the 6" gaps. I put in some corsican mint in one of the gaps. There is about 2-3" of growing room. Still thinking about what to do for the last one. Maybe periwinkle?
Thanks, again.

Because you have a contained area, any of the aggressive spreaders would work. Bishop's weed, creeping Jenny, english ivy, mint. etc...

Maybe some low growing spring bulbs for a little color.

Some others:

Lawn chamomile
Selaginella types
Vinca minor
Low growing sedums - I have some of the last two plus some mint and english ivy if you want to come to Cherry Hill and perhaps trade.

painfully clear I do not pay close attention.
Vinca would soon extend itself and you would constantly have smashed growth.
Try to find the 'stepables' website and consider some of their many offers. They do not sell directly, but local plant nurseries sometimes have a collection of what they grow. I think the website has a place to put in zipcode to find a local seller.

Creeping or woolly thyme spread, stay low-growing, and look and smell pretty. They are supposed to be tough enough to endure being walked on frequently, so they might be good choices for a driveway.

I'm bumping this, wondering what the questioner ended up with. I have a similar situation. A 3' x 15' strip between two brick parking surfaces.