The Commodore 64 has two 6502-family CPUs. There's a 6510 on the main logic board, and there's another CPU in the 1541 disk drive. The KERNAL on the host treated the 1541 as what is now called network attached storage (NAS), sending file access commands to CBM DOS in the 1541's ROM. Because the transfer protocol in CBM DOS was so slow, many C64 users sent a "fast loader" patch to the 1541's RAM in order to make data transfer faster. The demoscene eventually figured out how to run an interrupt-driven custom DOS in the background to stream data off the disk while animation continued on the host.
Fourth-generation game consoles
The Super Nintendo Entertainment System (called Super Famicom in East Asia) has two 6502-family CPUs. One is a second-source 3.6 MHz 65816 core licensed from WDC, combined with a DMA controller in the 5A22. The other is a 1 MHz Sony SPC700, which behaves as a 65C02 with reshuffled opcode numbers. Games run game logic on the 65816 and the sound engine on the SPC700. Some Game Paks include a third processor: either an NEC uPD77C25 DSP, a Capcom CX4 (Hitachi HG51B169) DSP, an Argonaut Super FX Graphics Support Unit (GSU), an SA1 (a 10.5 MHz 65816-based coprocessor), or even the entire Game Boy system-on-chip. (Source: "SNES Cartridges" in Fullsnes)
The Sega Mega Drive (called Genesis in North America) and Neo Geo AES have a similar setup, with a 68000 to run the game and a Z80 to run audio. The Sega CD and 32X peripherals add additional CPUs, and the game Virtua Racing contains an additional "SVP" CPU, analogous to the GSU.