The Electrum wallet, which is as ancient as Bitcoin, was designed to fit within the bitcoin specifiaction. Electrum wallet, which was first released in 2011, is a coin-specific wallet, meaning it only supports one coin: bitcoin. I didn't use this wallet much because it wasn't one of my favourites, but I was impressed with what I saw. Electrum wallet is a fairly simple wallet to use.
It has a mobile application that is Android compatible. It's a security-focused wallet that employs password protection to prevent unwanted access. This wallet is an opensource wallet, which means I can test it for flaws.