The best software which may fulfill your requirements is Trillian, filled with features, user friendly/enhanced UI, free (premium if you need some extra features).
- Facebook - Yes
- IRC - Yes
- Skype - Yes
- Whatsapp - No
I will come to the Whatsapp later, but as far as the features go for Trillian its packed with the ones you would expect from a decent "all in one" chat client.
Screenshot for an extensive list of clients supported by Trillian:
Features of Trillian
Your chats go with you everywhere. Trillian even keeps your phone quiet when you're active at a desktop!
With support for Google Talk, Facebook, MSN, AIM, ICQ, Yahoo!, and more, stay connected with everyone.
Trillian is available on Windows, Mac, iPhone, iPad, Android, BlackBerry, and directly in your web browser.
POP3, IMAP, and native IM mail integration. New mail alerts and basic mail management are all exposed.
Never miss a beat with Trillian's social integration, keeping you connected to Facebook, Twitter, and LinkedIn.
Keep your desktop tidy with tabbed chats, featuring drag and drop support, unread indicators, and more.
All desktop versions of Trillian come with a fully-featured message history viewer, including searching and filters.
Trillian's integrated spellcheck will always let you know when a word is misspelled and offer suggested fixes.
Hundreds of amazing handcrafted emoticons for your chatting pleasure. Find them all, even the hidden ones!
New to Trillian 5.3 for Windows, you can now chat directly in full-screen games with our awesome in-game chat feature.
Our skins and themes let you personalize Trillian for Windows any way you'd like. Change colors to suit your mood!
User-created language packs and strong UTF-8 support help ensure a great experience in your native language.
Coming to WhatsApp: You won't get any client whatsoever supporting this service on Computers, but there are various ways to achieve so, but make sure before you adapt any of the below steps as I was banned while doing so …
Now here this is a free software to install mobile apps on your computer. So using BlueStacks, you can install whatsapp on the software and use it from your computer after you receive a verification code from WhatsApp.
This will do same as the above, but this app is somewhat useless..I've used this, I cannot install games, no software, nothing, but I did ran WhatsApp and I was banned after few months.
So choose wisely and again I would like to alert you that be cautious using WhatsApp from your computer.