Learn that:

Unlicensed software is not just murky, it's illegal
AGPL is used by over 1% of projects (read the talk to learn why this is bad!)
If a maintainer sends malware to you through their package... you can't sue them!
Under a certain license it is illegal to use that software while alive...
Some projects, notably Perl, continue to use a license that predates even GPL
Some projects knowingly breach licenses... who's gonna sue em!
Spigot uses Bukkit off of a technicality

And more...

Download links are at the top for both PDF and ODP.