cfssl

https://github.com/cloudflare/cfssl

CFSSL consists of:

• a set of packages useful for building custom TLS PKI tools
• the cfssl program, which is the canonical command line utility using the CFSSL packages.
• the multirootca program, which is a certificate authority server that can use multiple signing keys.
• the mkbundle program is used to build certificate pool bundles.
• the cfssljson program, which takes the JSON output from the cfssl and multirootca programs and writes certificates, keys, CSRs, and bundles to disk.

Possibly, freedom from the openssl CLI, which is without question the worst CLI interface I have ever used. It makes git look positively user-friendly.to