Parity Signer Companion is a Chrome extension developed by Parity Technologies. It is a free add-on in the Browsers category, specifically under Add-ons & Tools. This extension is designed to inject your Polkadot accounts from Parity Signer and allows you to securely sign transactions.

The main purpose of Parity Signer Companion is to help users sign transactions using the keys stored in the Parity Signer. In order to start using this extension, you need to go to the Signer and import your keys. It is important to note that without the Signer, this extension is rendered useless.

If you are looking to create and store keys without any device, you may want to consider using the Polkadot{.js} extension available on GitHub.

Parity Signer Companion is a reliable tool for securely signing transactions with the keys stored in Parity Signer. It provides an added layer of security for Polkadot users, ensuring that their transactions are protected. However, it is important to note that this extension is dependent on the Parity Signer and cannot be used independently.