debug - Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
doc - Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally
gnutls - Prefer net-libs/gnutls as SSL/TLS provider (ineffective with USE=-ssl)
sodium - Enable support for Argon2 password schemes using dev-libs/libsodium
ssl - Add support for SSL/TLS connections (Secure Socket Layer / Transport Layer Security)
