On iOS (and beta for macOS) I can't recommend OTP Auth[1] highly enough.
It does one thing and does it well. For a business/team case (i.e. if an account must be shared) I'd probably stick to Pass[2] with the OTP plugin[3] but for 99% of use cases, OTP Auth wins hands down.
1: http://cooperrs.de/otpauth.html 2: https://www.passwordstore.org 3: https://github.com/tadfisher/pass-otp#readme
There's also _totp-cli_, which also uses _pass_ as a backend. The big difference is mostly that _totp-cli_ uses a more human-friendly interface, rather than requiring machine-friendly input. It also predates pass's support for plugins.