Uses the latest GPL audio codecs, such as Opus, an adaptative high-quality codec that supersedes AAC at any bitrate.

You can pin messages to the top of groups or supergroups so members will see them when opening the group.

You can write messages to yourself. You can write some notes, add links, and see everything across all your devices.

Although it's volunteer based, but still pretty top-notch if available, which it tends to be.

Unlimited number of files can be stored forever on the cloud. You can upload files up to 1.5 GB each.

You can ping people to get their attention by @mentioning them.

You can post voice and video messages if you are too lazy to write text messages.

There are native desktop, mobile and web client apps, that are optimized for speed and are light on memory usage.

Client apps are open source, making whole service more trustworthy.

Works on Windows, Mac, Linux, Android iOS, Windows Phone, and Firefox OS even. Has a web app that changes it's appearance based on the device it's running on and if it's browser is full screen, etc.

In Supergroups, anyone along with admins can delete their messages from all sides. A message can be pinned to the top. All of the user's messages can be deleted by an administrator, and they can be banned and reported as well. Supergroups can have a public link (outside of Asia, due to high spam volumes), which is also a username.

Very customizable with a lot of clean looking options.

Videos, gifs, images, geolocation, and documents.

Copy/paste videos, gifs, images, geolocation, documents, and even executable files. Drag over files for practically any time up to 1.5GB in size. Images can be compressed, too.

Unfortunately, on the desktop videos don't play, but images are viewable without visiting popular websites like imgur and Instagram.

You can play YouTube videos and others within the app, so you don't need to embed code or anything.

With inline bots, such as @gif, @pic/bing, @vid/YouTube, etc, you can look things up without leaving the client or chat that you're in. Simply type the name and some keywords and wait for the results to load.

Telegram uses an open source MTProto encryption protocol that provides complete end-to-end encryption for secret chats. To show off their confidence in the protocol the company behind Telegram has organized $200,000 and $300,000 challenges to break the encryption. So far there have been no winners.

You can set up an additional password to your account, which can be reset by your email. You don't have to use an email if you do not want to. If you lose access to your email or forget your password, you will be able to reset it via text message if your account is over seven days old and will receive it within a week (in case you recover anything before then).

Broadcasting channels suitable for announcing things.

The application is available free of cost.

In addition to the end-to-end encryption that provides privacy to communications, the app also includes self destructing timers for chats, and the ability to permanently delete messages, yours and theirs, from your device.