Channels & DMs
Public and private channels, 1:1 and group DMs, unread badges, @mentions, @here and @channel.
Team chat you own.
On your own Firebase project.
Channels, threads, DMs, search, reminders and push notifications, deployed to your Google Cloud project with one command. Pay-as-you-go, and a small team usually pays $0.
Free & open source · Built for teams of 10–100 people, or more · Invite-only
Everything a team actually uses
The Slack features you'd miss, none of the seat fees.
Threads
Reply in threads, “also send to channel”, and see who's typing, even inside a thread.
Search everything
One shortcut for channels, people and messages. Filter by person, channel, date or files.
Reminders & scheduling
/remind me in 1h to…, /schedule tomorrow 9am…, snooze, and a Later inbox.
Real push notifications
Desktop, Android and iPhone home-screen app. Per-channel levels and Do Not Disturb schedules.
Reactions, pins, saves
Your own quick reactions, pinned messages per channel, mark unread and save for later.
Presence & status
Online, away when idle, last seen, custom status with expiry, local time on every profile.
Files & link previews
Drag, drop or paste files up to 50 MB. Links unfurl with title, description and image.
HTTP API
Post from CI, scripts and bots, read channels and search with personal tokens. API docs
Ask Flackbot
Optional AI: ask what your team decided and get a short answer with links to the messages. It only sees what you can see.
Flackbot
Reminders arrive in a DM with Snooze, new members get a welcome, and your own automatic answers to common questions.
Your brand
Your workspace name, logo, colors and sign-in message, set by admins in a couple of clicks.
Ask Flackbot
Answers from your team's own conversations.
Ask “what did we decide about pricing?” or “what did I miss today?” in a pane next to your channels (full screen on phones). Flackbot searches and reads the messages, then answers in a few lines with links to its sources.
- Only sees what you can see. Its searches run as you, with the same checks as the app, and it can't post or change anything.
- Claude on Vertex AI in your own Google Cloud project. No API key and no extra vendor bill: a typical question costs 2–5¢.
- Off until an admin turns it on, with a daily limit per person and a monthly budget that pauses it.
Install
From zero to your own chat in about 15 minutes.
-
1
Get the code
Click Install in Cloud Shell (nothing to install, you're already signed in), or clone it:
git clone https://github.com/mvergarair/flack cd flack -
2
Run the installer
It asks for a project id, region, your email and a budget, then sets up and deploys everything.
npm run setup -
3
One click, then invite
Enable Google sign-in in the Firebase console (the installer prints the link), sign in, and invite your team from Admin.
The installer creates the project (or uses yours), links billing, turns on Firestore, Realtime Database, Storage, Functions and Identity Platform, writes the config, sets a budget alert and deploys. Safe to re-run.
Cost
Pay-as-you-go, sized for $0.
Flack needs Firebase's Blaze plan: no monthly fee, you pay only for usage beyond the free quotas, which reset every day or month. Flack is built to stay inside them: 50-message pages, an offline cache, presence and typing in the Realtime Database, and search that scales to zero.
The installer sets a budget alert (US$5/month by default) that emails you at 50%, 90% and 100%. The one line item you'll usually see is a few cents a month for storing function images. Ask Flackbot is optional and billed per question (about 2–5¢ with Claude Sonnet 5.5), capped by a monthly budget you set.
A busy 25-person team, per day
Database reads~20k of 50k free
Database writes~3k of 20k free
Function runs~3k of 66k free
Stored files~1 GB of 5 GB free
Realtime traffic~1 GB of 10 GB/mo free
Estimates; usage varies with how chatty your team is. Beyond the free quotas you pay a few cents per 100k database operations and about $0.02–0.03 per GB of files per month.
Security
Your data stays in your project.
No middleman
Everything lives in your Google Cloud project. There's no Flack server and no third party.
Rules on every read
Firestore, Storage and Realtime Database rules check the invite, the role and channel membership on every request, with 100+ automated tests.
No public file links
Files download through the SDK with the rules applied. Nothing has a guessable public URL.
Invite-only sign-in
Blocking functions refuse any Google account that wasn't invited, and deactivated people are locked out immediately.
Flack in numbers
–teams running Flack (last 30 days)
–most common team size
–use push notifications
–most used version
Anonymous, aggregate numbers from installs that share usage statistics (on by default, easy to turn off; never messages or names). See all numbers · What's collected
Questions
Do I need a credit card?
You need a Google Cloud billing account (Blaze plan) because Flack uses Cloud Functions. With the free quotas and the budget alert, small teams typically pay nothing.
How many people can use it?
It's built for teams of 10–100 people, and larger teams work too. Past a few hundred people, the repo's backlog describes how to trim the always-on listeners (presence and the member directory) to keep costs flat.
Can I use my own domain?
Yes. Add a custom domain in Firebase Hosting and add it to the authorized domains for sign-in.
Is it a real app on phones?
It's an installable PWA: add it to the home screen on iPhone or install it on Android for push notifications and a full-screen app.
What does Ask Flackbot send to the AI?
Only what it needs to answer: the question and the messages its searches find, all from channels the person asking can already read. It runs on Claude through Vertex AI in your own Google Cloud project, under Google Cloud's terms. It's off by default; turning it on needs a one-time "Enable" for the Claude model in Vertex AI Model Garden and some Vertex AI quota (the installer requests it).
How do I update?
Run npm run update in your Flack folder. It pulls the latest version, turns on anything new it needs and deploys, keeping your settings. Admins see a note in the app when a new release is out.