A convenience and ease-of-use layer for use on top of dm-crypt.
Gentoo maintains a guide for dm-crypt with LUKS.
Arch Linux also maintains a guide to dm-crypt with LUKS.
Slackware Linux also maintains a guide to dm-crypt with LUKS.
dm-crypt is available for DragonFly BSD.
Disclaimer: Using the recommended projects on this site will not guarantee that 100% of your communications will be shielded against surveillance states. Please do your own research before trusting these projects with sensitive information.