Investing in Private Equity or other Off market investments?

Anyone invest with private groups outside of the markets?

I remember many years ago (decades) coming across some company that made all kinds of wild investments. I think they down 40% one year, but up big over the previous decade. Had some crazy minimal investment.

I was just thinking about how I see stories about Private Equity investments and acquisitions all of the time. But really don't know much of anything about the space.

Are there any good websites out there for investment opportunities? Are these usually just fronts for other companies? I just read an article about PE buying up Veterinarian offices. But the same article said that a big chunk of that was literally the MARS candy company. Obviously something that you can't just go invest in.

Are there terms that split the PE groups into big companies looking to invest their own money vs private funds that allow outside investment? Any info to learn more about the space would be greatly appreciated.