Series of portable computers, from Commodore, introduced in 1983. The first machine was called Commodore SX-100, but it eventually became Commodore SX-64, aka Commodore DX-64 (same machine, two floppy drives).

Basically, these machines were Commodore 64s in a portability-enhanced chassis, no Datassette port, and built-in floppy drive and CRT (yes, youngsters, back then LCD displays were a myth!) OS was hacked a bit: Screen colors were different, the startup messages were different and loading defaulted to device 8.

Note the subtle naming... Commodore obviously knew that laptop machines would have a market!

See also: Osborne 1

A few notes:
All cassette routines were removed from the kernel, and the Commodore DX-64 wasn't really ever released into the public as the machine's power supply couldn't handle two floppy drives.
There are official C= upgrade kits floating around in Germany, that allow you to convert your SX into a DX.

Today, a fully working Executive 64 with no broken plastic bits is pretty much the holy grail for Commodore collectors in their quest for rare Commodore hardware.

They sell for around $100 on e-bay so if you've got one in the attic/basement/garage collecting dust and you have no heart, sell it. Preferably to me.