The SLAB_USBtoUART is a USB to Serial device. SLAB is short for SILABS, the chip inside of this device.
Linux 2.6.x: linux_2-6-x_vcp_driver_source
Linux 3.x.x: linux_3-x-x_vcp_driver_source
Windows CE 6.0: vcp_wince60
Windows CE 5.0: vcp_wince50
Macintosh OSX (v4): mac_osx_vcp_driver (confirmed to work with macOS Sierra)
Windows 2K Server Download VCP (4.79 MB): cp210x_vcp_win2k-exe
Windows XP/Server 2003/Vista/7/8/8.1 Download VCP (3.66 MB): cp210x_vcp_windows
Windows 7/8/8.1/10 Download VCP with Serial Enumeration: cp210x_windows_drivers_with_serial_enumeration
Windows 7/8/8.1/10 Download VCP (5.3 MB): cp210x_windows_drivers
On OSX / Linux you may find the device listed under /dev/tty.SLAB_USBtoUART or /dev/cu.SLAB_USBtoUART
If you are installing these drivers as part of a Pulse Oximeter, you should check out this post which gives a little more info for that domain.
Unsure what operating system you have? Check out http://whatsmyos.com/
The drivers listed above are sourced from Silicon Labs. They are kept here as a mirror of the silicon labs driver page. I will do my very best so that any links to this site will not be broken. Questions or Answers? Please comment below.