Where I live, a lot of people use Telegram. It has less cluttered interface and is also much faster than WhatsApp on unreliable connections.
MySMS is a similar service that also enables to send text messages via a desktop (web) application. I've been using it for a while. It can be a bit buggy though - not as polished as Whatsapp.
Don't they literally all do it? Line, KakaoTalk, WeChat, iMessage, BBM...