MMGen Wallet implements Monero 'offline transaction autosigning'
Cold signing of Monero transactions with maximum convenience. [..] A unique security feature is that signing wallets are created afresh in volatile memory for each transacting session and thus disappear when the signing machine is powered down.
mmgen-xmrwallet --help for documentation about offline autosigning in MMGen. For general information about Monero offline signing, visit monerodocs.org3.
To support the project, transfer some XMR to the donation address listed at the bottom of the README.md4 file on Github.
Consult the previous Monero Observer report5 to learn more about MMGen.
Note: inspect the code before using, if you can read Python.