When comparing IRC vs Flowdock, the Slant community recommends Flowdock for most people. In the question“What is the best team chat software?” Flowdock is ranked 4th while IRC is ranked 12th. The most important reason people chose Flowdock is:
An easy & simple interface to filter chat discussion into separate threads.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Open protocol
The IRC protocol is public and open, it is mature and stable, and has been implemented in numerous projects. This means that it can be used freely, for both open-source and commercial projects.
Pro Versatile
IRC offers choice. Choice in clients (mobile, desktop, web), in scripts those clients run, in servers and features those servers have. You can even set up your own server.
Pro Less distracting
Compared to other common solutions, IRC can be ignored when you are occupied doing something else. Most clients don't pester you with sounds or distracting visuals.
Pro Mentions
Every notable IRC client supports mentions - notifying you when your name is mentioned in the chat. The mentions in IRC are comparably better than Discord. Mentions used in Discord are easily abused; this doesn't happen in IRC. If someone's talking about you, you get a notification in IRC. This doesn't happen in something like Discord.

Pro Hundreds of avaliable clients
IRC has been around since 1988, so there is a ton of existing software to work with it. Everything from clients, to chat bots, to bouncers is already built.
Pro IRC networks are not centralized
You can choose your favorite server for an IRC network.
Pro No account necessary
No need to sign up for access, confirm your e-mail address. Just choose a nickname and you're done.
Pro User-friendly
IRC is user friendly if you use something like hexchat or kiwi webchat.
Pro DCC
Direct Client-to-Client allows users to share files in a similar way to torrenting.
Pro Great historic importance
Twitter hashtags came from IRC channel names.
Pro Upcoming IRCv3 will provide missing features

Pro Threaded discussions
An easy & simple interface to filter chat discussion into separate threads.
Pro Drag and drop file sharing
Files can be dragged and dropped in to the flow dock screen for upload.
Pro Multi-platform
Browser Based, as well as:
- iPhone and iPad App
- Android App
- Mac OS X App
Pro Stored chat history
Content and discussions are stored forever.
Pro Smart pastes & code syntax highlighting
Pro Private chat option
Able to speak privately/talk head-to-head.
Pro Notification system
A specific user or everyone in the channel can be notified via @user or @everyone respectively.
Pro A full developer API
Flowdock API allows developers the freedom to create custom integrations.
Pro Create and assign PRs from Flowdock
You can interact with Github directly from Flowdock to create PRs.
Pro Free for teams of five, non-profits and students
Pro Data exports
Back up conversations and files fully at any time.
Pro Add Tools
On top of our 50+ custom integrations, easily integrate any tool that sends emails or generates RSS feeds, as well as having the option to build a custom integration with Flowdock's API
Pro Status updating
Allows co-workers to know what you’re up to "/status I'm busy today!"
Pro Google Apps Integration
Google Apps get a Flowdock link to the Apps tool-bar and won't have to separately manage users
Pro Typo Fix-ups
Pro Able to host users external to your team
When working with stakeholders (clients or partners) you can add organizations to manage internal privacy
Cons
Con Complex and not user friendly
Con Assumes some level of prior knowledge
The features are not discoverable the way they are in other apps and services.
Con You have to "idle" to see what's going on
You will see a blank chat screen at first because there is no recent history kept on servers.
Con Can be addictive
Con Poor multimedia support
Sending anything besides text is not easy or intuitive and depends on the client.
Con Advanced functionality is client-dependant
Con Proprietary (non-free/libre)
Con No self-hosting available
If you are worried about third-parties getting access to your data you should consider self-hosting. With self-hosting you are in control over where your data is stored, who has access to it. You will also not be vulnerable to exploits of a third-party provider.
Con Buggy android app
Google sign up didn't work, then after going to the website to do the sign up, the invite team members screen was broken.
Con Free only for small teams, non-profits or students
Unless it's used by a team of less than five people, a non-profit or students, Flowdock will cost $3/mo per person.
