Cirrus Insight is purpose-built for Salesforce productivity, activity auto-logging into Salesforce contact and opportunity records, calendar scheduling bound to Salesforce calendars, native Outlook and Gmail add-ins, with email tracking bundled in. The pricing (per feature seat, with Buyer Signals at $10/user/mo on its pricing page) is fair for the Salesforce-sync depth but expensive if Salesforce sync is not the load-bearing reason your team is on it.
These are the five Cirrus Insight alternatives worth evaluating, organised by whether Salesforce sync is the deciding feature or whether tracking and engagement features matter more.