Telegram released a stable version for desktop 1.0. It was available on desktop and laptops since 2013. It's common along all the three Windows, Mac and Linux. Although there is already an official app available on the Mac App store that has native macOS UI design and features. Only Telegram knows what's gonna happen to that. Telegram insists on Using the new one. If you like the older app then keep using it till it works.
What makes Telegram different from others desktop app is that it syncs messsages from your phone with your computer using Telegram's encrypted cloud. Install it and log in to your account and all the messages , documents, photos and videos will be synced from your secure cloud. It also features like, you start typing on your phone and continue it on from your desktop.
You can download it from here.