xf86-video-vesa
X's last resort on a PC: a driver that knows nothing about the graphics card, asks the BIOS for a video mode and draws everything else in software.
Every PC graphics card since the 1990s implements the VESA BIOS Extensions, a standard way to change video mode through the BIOS and get a linear framebuffer. The vesa driver uses nothing else: it calls the BIOS through an x86 emulator, picks one of the modes the card advertises, then draws everything with the CPU, preferably via a shadow buffer in ordinary RAM because reading back from the card is slow. No acceleration, no 3D, no extra monitors.
That was enough for installers, virtual machines and new cards that had no driver yet. It often produced 1024×768 on a screen that wanted something wider, because the BIOS had never heard of the laptop panel's native resolution. On UEFI-only machines there is no BIOS to call, and modesetting and fbdev have taken over the role.