SI
Signal
Best for: End-to-end encrypted private messaging
Open SourceFree
Signal is the gold standard for private, end-to-end encrypted messaging. No ads, no data collection, funded by a nonprofit. Supports text, voice, video, groups, and file sharing with state-of-the-art encryption.
- Gold standard for private, end-to-end encrypted messaging
- No ads, no data collection, funded by a nonprofit
- Supports text, voice, video, groups
Free tier: Listed as free — verify limitsPricing: Free (open source, donation-funded)
SL
Slack
Best for: Team messaging
Free
Slack is the leading team messaging platform. Channels, threads, and deep integrations with 2,400+ apps make it the default communication layer for tech companies.
- Leading team messaging platform
- Channels, threads, and deep integrations with 2,400+ apps
- Free tier available
Free tier: Listed as free — verify limitsPricing: Free / $7.25/mo Pro / $15/mo Business+
DI
Discord
Best for: Communities and async teams
FreeBest Value
Discord started as a gaming chat platform but is now used by developer communities, open-source projects, and remote teams. Its voice channels and community features are unmatched.
- Persistent voice channels — join anytime, like a virtual office
- Threads, forums, and stages for structured async communication
- Generous free tier with no message history limit
Free tier: Listed as free — verify limitsPricing: Free / $9.99/mo Nitro
MA
Mattermost
Best for: Mattermost is an open-source Slack alternative built
FreeOpen SourceBest Value
Mattermost is an open-source Slack alternative built for teams that need full data control. Deploy on your own servers with enterprise-grade security and compliance.
- Self-host on your infrastructure — complete data ownership
- Slash commands, bots, and integrations similar to Slack
- SOC 2 and FedRAMP-compatible for regulated industries
Free tier: Listed as free — verify limitsPricing: Free (self-host) / $10/seat/mo Professional
RO
Rocket.Chat
Best for: Open-source team messaging
FreeOpen SourceBest Value
Rocket.Chat is a fully open-source communications platform with messaging, video calls, live chat, and omnichannel support. Self-host or use their cloud.
- Omnichannel — handle team chat and customer support in one app
- Built-in video conferencing with no third-party required
- 800+ community apps and integrations
Free tier: Listed as free — verify limitsPricing: Free (open source) / Cloud from $7/seat/mo