In a nutshell RPCS3 is simply a kick-ass emu!
A passionate team of very talented developers is after the gigantic project of accurately emulating what's inside the PS3's heart, the CELL microprocessor. At the time of writting the RPCS3 emu has almost 48% of the PS3 game library at a playable state. You can find very interesting information in the official RPCS3 about info page but what you need to know really is that this PS3 emulator is no joke, it's all business and you'll have lots of fun trying out your PS3 games on it. And by "it" I mean one of it's supported platforms which are Windows, Linux, macOS and FreeBSD.
One little fun fact is that Emunewz hosted the official forums of this wonderful emulator in it's infancy years.
We also have a very nice interview with the RPCS3 team but oh boy it has gotten so old!!! We have to make a new one!
RPCS3 Official site
RPCS3 Official Github page
RPCS3 Discord