Bisq is described as 'Desktop peer-to-peer (P2P) application that allows you to buy and sell bitcoins in exchange for fiat (national currencies), or alternative crypto currencies' and is a popular cryptocurrency exchange in the bitcoin & cryptocurrency category. There are more than 100 alternatives to Bisq for a variety of platforms, including Web-based, Android, iPhone, iPad and Mac apps. The best Bisq alternative is Unstoppable Wallet, which is both free and Open Source. Other great apps like Bisq are Coinbase, Blockchain Wallet, LocalCoinSwap and AgoraDesk.
I don't like Unstoppable Wallet as an alternative to Bisq because they are not similar enough. Bisq is P2P local bitcoin exchange while Unstoppable Wallet is not an exchange whatsoever but simply a wallet.