Slack

Slack defined the modern channel-based messaging category when it launched in 2013, and its network effect has made it the default for a generation of knowledge workers. The concept is straightforward: conversations are organized into channels — public, private, or shared across organizations — with direct messages and group threads layered on top. What keeps teams inside Slack is the integrations: more than 2,600 apps connect GitHub, Jira, Salesforce, PagerDuty, and virtually every other SaaS tool in a typical stack, turning channels into lightweight ops dashboards rather than simple chat rooms.

Salesforce acquired Slack in 2021 for $27.7 billion, and the two platforms have since deepened their integration around customer workflows and CRM data. Slack AI, introduced in 2024, adds channel summaries, thread recaps, and search over message history.

The cost calculus is where teams start doing the math. Pricing begins at $7.25 per user per month (billed annually) for the Pro plan, which unlocks full message history — the free tier caps it at 90 days and 10,000 searchable messages. For a 50-person team that is $4,350 per year before any add-ons. There is no self-hosting option, so data residency requirements or airgap mandates push organizations toward alternatives. Those constraints — per-seat billing, no data ownership, and a free tier deliberately limited to drive upgrades — are the primary reasons teams evaluate open-source substitutes.