The Telegram web-client is a free, fast and secure way to enjoy most of Telegram's features right in your web-browser.
It is always synced with the Telegram app on your mobile device, which makes it a perfect tool for messaging and file sharing.
"Franz is your messaging app / former Emperor of Austria and combines chat & messaging services into one application. Franz currently supports Slack, WhatsApp, WeChat, HipChat, Facebook Messenger, Telegram, Google Hangouts, GroupMe, Skype and many more. You can download Franz for free for Mac & Windows."
"Delta Chat is like Telegram or Whatsapp but without the tracking or central control. Check out our GDPR compliancy statement. Delta Chat doesn't have their own servers but uses the most massive and diverse open messaging system ever: the existing e-mail server network. Chat with anyone if you know their e-mail address, no need for them to install DeltaChat! All you need is a standard e-mail account."