It's a free IRC client supported by donations.

AdiIRC is constantly being developed and improved. It's among the most actively developed IRC clients nowadays, with a great beta team behind it. The changelog shows multiple substantial releases every month.

It works perfectly with Windows 10, has all the needed functions like:
1 - handle all irc:// links.
2 - start with windows.
3 - start minimized.
4 - close to tray icon when pressing X(close button).
5 - it can open all the channels in one window or open each channel in new windows (it is up to you).
6 - tons of options to pick up from.

Feature requests, suggestions and bug reports get prompt feedback.

A portable version is also available in the download section. It can be run without installation allowing it to be run off of external devices such as USB sticks.

miRC themes also works well in AdiIRC.

The vast majority of mIRC scripts/snippets work in AdiIRC, with compatibility constantly being improved.

Supports Foobar2000, Winamp, QCDPlayer, iTunes, MusikCube, MediaMonkey, XMPlay, Spotify, VLC Media Player, Media Player Classic, MusicBee, PotPlayer and SMPlayer.

Inline support for custom emotes and icons. Adding , removing or editing images replaces whole chat buffer tags in real time. AdiIRC makes your irc experience much more fun.

(unlike hexchat which needs to manually add a script)

Spellcheck for over 120 different languages is available. Full list of languages can be found here.

Plugins support too, with certain scripting languages to write.

The client weighs less than 1MB.
Low CPU usage. Almost no CPU usage, in fact...

Nick Column feature support too.

You choose, Simple or Complex layout. Check the screenshots section in here.

You can modify or add your own hotkeys to your desire function.

It can be updated via updater or via command fast and easy.

You can create your own theme easy...

You can monitor any event you like via dock panels too.

Configurations, scripts and snippets are saved within the installation folder, allowing you to easily move them to a different installation. It also means that nothing is changed in your system.

Does not create registry keys.
Does not create any other folder than it's own on any other location.
Even when the installer is used, you can make it portable by just moving the folder around, don't need to worry about anything else.

GUI translation available in several languages with contribution by users around the globe in an online web interface found here.