Get temporary & limited access to your friend's MetaMask wallet without ever receiving his private keys.
The RemoteSign Extension can be used as a MetaMask Extension alternative along with an access key.
As the owner of an Ethereum wallet, you can use remote-sign.com to generate access keys, which grant limited access to your wallet, without ever handing over your private keys.
How it works:
1. Connect to remote-sign.com with your MetaMask and generate one or more access keys, with each access key being connected to an Ethereum address.
2. Hand over the access key(s) to your friend who should get (limited) access to the Ethereum address the access key belongs to.
3. Your friend installs this extension and enters the access key.
4. He can now use this extension to do stuff in a similar way as MetaMask would be used.
5. The RemoteSign extension forwards requests to remote-sign.com, where you can answer the requests with your MetaMask to approve your friend's requests.
Note: The extension is under active development and may contain errors.