Assuming that there is an ERC20 compatible token deployed on the Ethereum blockchain, is it possible to:
1. Have a stand-alone wallet solely for this token (not an Ether wallet + watching a token, but a dedicated app). Maybe some existing open source solutions?
2. Is it required to download the full Ethereum blockchain in order to be able to send\receive those custom tokens?
ERC20 – Is a Stand-Alone Wallet for an ERC20 Compatible Token Possible?
erc-20wallets
Best Answer
Yes.
No. You can run a lightwallet.
Iconomi released an ERC20 Token (ICN) and has an ICN-only wallet available via their ICO page. I do not believe it's open source, but they do have a contact page.
Alternatively, ConsenSys has published an Ether Lightwallet (MIT License) - although, this would be an Ether wallet + watching a token.