YAP64 was the Nintendo 64 portable I built years ago. Features include stereo sound, a 3.5″ LCD screen, twin analog sticks (switchable), a non-working docking connector, and the theoretical ability to play and charge at the same time (it never worked).
YAP64 really wasn’t very good. It was huge, it was heavy, it was a battery pig, and it broke easily. It suffered from feature creep, procrastination, and a general lack of skills. Still, it was a learning experience, and I later built stuff that looked and worked much better.
I had intentions of building another, vastly improved portable, but I didn’t get very far before losing interest. I eventually got a smartphone, which emulates the N64 acceptably and actually fits modern definitions of portable.
There is another portable called YAP64 out there. This is the original, but I won’t blame you for accepting the substitute.