Self-hosted session replay has a new contender, and its architecture is doing something the SaaS incumbents don't.
The founders of S2, a streaming infrastructure startup, released RePlaya: an open-source browser session replay tool built on rrweb, the same recording library that powers parts of PostHog and others. Instead of the standard ingest-and-index pipeline (message queue, metadata database, blob storage, maybe an OLAP layer), RePlaya maps one durable S2 stream to each browser session. That single-stream model is what makes live tailing cheap: the player reads from the same stream the recorder is writing to, bridged to the browser over server-sent events with no extra coordination. The only hard dependency is S2 itself, which has a self-hostable open-source edition called s2-lite.
For teams under GDPR, HIPAA, or other data-residency constraints, self-hosted session replay is a meaningful option. Most of the market (FullStory, Hotjar, LogRocket) defaults to SaaS, which means user interaction data leaves your infrastructure. Self-hosted alternatives have historically inherited the same multi-system complexity the SaaS products paper over; RePlaya's argument is that a single streaming primitive can replace that stack.
Worth keeping in mind: RePlaya is also a showcase for S2's own infrastructure product. The founders have clear incentive to make the stream-per-session model look appealing, which doesn't make the architecture wrong, but does mean the comparisons to the "alternative" approach deserve some scrutiny before you swap your existing stack for this one.