Telegram has released the version 1.0 update of its universal desktop application, Telegram Desktop. The app had been available for a while but this is the first stable release and it comes with a new UI.
Common across all three versions is the use of Material Design. This doesn't really make the app look at home on any of the support desktop operatings systems but at least Material Design is mostly unobtrusive and inoffensive.
The app also has support for theme and you can join Telegram's Theme Channel to get some of the alternative themes. Apart from that, the functionality is consistent with all the other Telegram apps, including syncing of all your messages and support for stickers, gifs, bots and all sorts of things. You can even start typing on your phone and continue on the desktop because the apps sync typed text.
For Mac users, there is already an official Telegram app available on the Mac App Store that actually has native macOS UI design and features. It's not sure what will happen of that, but Telegram insists the new Telegram Desktop is the one to get. For now the two seems similar in functionality (except for the presence of themes on the new app) so if you want to retain the native look and feel of the older app then you can probably keep using it as long as it works.
Maybe they'll now implement the most requested feature : Secret chats (https://github.com/telegramdesktop/tdesktop/issues/871)
You can introduce it to your circle and they to others and so on. It may never catch on like WhatsApp but it'll be an alternative you can work with if ever WhatsApp (or your favourite IM app) gets blocked in your country.
Too bad almost nobody in my country uses Telegram...