Scrit (also referred to as Scrit1), which is referenced as "prior art" for Fedimint, has methods for "half-offline" (i.e., only sender online, or only recipient online), and offline (i.e., both offline, and could be done via paper / QR codes even).

"Scrit: A distributed untraceable electronic cash system" https://github.com/scritcash/scrit-whitepaper/blob/master/scrit-whitepaper.pdf

The Fedimint homepage also refers to "Scrit2" with having "receiver- and sender-initiated half-offline transactions".

And along these lines:

Transferable E-cash: A Cleaner Model and the First Practical Instantiation https://eprint.iacr.org/2020/1400.pdf

And there are a number of redeemable code / voucher / etc approaches, including:

LNCash https://ln.cash/how