Can you recommend a user behavior analytics platform for measuring activation and retention in a mobile app?

Yes — for activation and retention in a mobile app, I’d recommend looking at Amplitude first.

Why Amplitude

• Strong event-based analytics: easy to track onboarding steps, feature usage, funnels, and drop-off points.
• Retention analysis: very good cohort retention charts and behavioral segmentation.
• Activation-focused workflows: helps define “aha moments” and monitor whether users reach them.
• Mobile-friendly: solid SDKs for iOS and Android.
• Product analytics + experimentation ecosystem: useful if you later want to connect analytics with feature flags or A/B tests.

Good alternatives

• Mixpanel: very strong for funnels, retention, and user-level behavioral analysis; often preferred for fast product iteration.
• Firebase Analytics / Google Analytics 4: good if you want a free or low-cost option and are already in the Google/Flutter/Firebase ecosystem, though it’s less product-analytics-friendly than Amplitude or Mixpanel.
• PostHog: great if you want open-source/self-hosted control and a broad product analytics stack.

If your main goal is specifically:

• Best activation/retention insights: Amplitude
• Simpler product analytics with great funnels: Mixpanel
• Lowest cost / Google ecosystem: Firebase Analytics
• Open-source / self-hosted: PostHog

If you want, I can also give you a side-by-side comparison of Amplitude vs Mixpanel vs PostHog for a mobile app.