Toshiba T7766A, Winbond WF19054, JFC 95101 and File KC89C72 are clones of the PSG. [https://wiki.agiri.ninja/sound_chip_clones:index Source]
The chip is clocked differently depending on the computer: ZX Spectrum: 1773400 Hz ; Pentagon: 1750000 Hz ; MSX: 1789772 Hz ; CPC: 1000000 Hz ; Atari ST: 2000000 Hz.
The PSG chip competed with the DCSG (Digital Complex Sound Generator) chip family (SN76489, SN94624, TMS9919) by Texas Instruments. The DCSG has similar sounding features except that it does not have any envelope control and that its noise generator has its own dedicated channel.