I recall this obscure yet fun game with simplistic graphics. It looked a lot like Crimsonland, but as far as I know, it had a campaign mode with bosses. The things I recall most vividly were skill trees with the respective playable character in the background, as well as a character that had dual miniguns(?) I used to get many games from the then-popular site caiman.us, so it might've been from there, but I'm... Source: about 2 years ago

Probably not as it's not (and never was) all black but http://caiman.us/ ? Source: almost 3 years ago

As far as I know the official site just stopped working and the download on gta5-mods.com doesn't work either. Source: 11 months ago

Lastly, I know gta5-mods.com is the go-to place for mods. I'm just asking these things because I can probably figure out the rest on my own without having to post follow-up questions. Source: about 1 year ago

Use scripthookV and download mods from gta5-mods.com. Source: about 1 year ago

I noticed that too after looking at the developer's website. The gta5-mods.com website, where I originally got it from, stated it was last updated in 2017. Source: over 1 year ago

You'll find most on gta5-mods.com by searching with the "vanilla edit" tag. Source: over 1 year ago