The energy was palpable yesterday at Replay ‘25 in London. As developers huddled around tables, keyboards clicking and ideas flowing, you could feel that special buzz when creative minds come together. Day one of our event showcased what the Temporal community is all about—building, learning, and solving problems together.
Unconference Hackathon: Community-Driven Innovation
The day kicked off with rapid-fire project pitches that set the tone for what would become a remarkable day of creation. Over 60 participants—ranging from Temporal newcomers to battle-tested veterans—voted on ideas they were passionate about, naturally forming seven distinct teams.
What happened next was fascinating to watch. Each table became its own innovation hub, with participants often splitting into smaller groups to tackle different aspects of their projects. As the day progressed, these parallel efforts merged into impressive demonstrations of what’s possible with Temporal.
Eight distinctive themes emerged: two AI-focused groups, Visualization, Finance, Gaming, Developer Experience, Batch Orchestra, and Microservice Orchestration.
AI was clearly a hot topic, but the range of projects showed the versatility of Temporal across different domains. From social media sentiment analyzers to auction systems, the creativity on display was impressive.
One standout project was a GUI Workflow execution visualizer that generated flowcharts showing exactly where in your business logic a Temporal Workflow is running. Another team built a visual “diff” tool that highlights changes between Workflow runs. The Batch Orchestra team focused on creating an easy-to-use library for reliably performing many like operations such as database migrations and periodic batch jobs.
Throughout the day, participants swapped ideas, troubleshot together, and built connections that extended beyond the code they were writing.
Demo Time: Creativity on Display
The afternoon culminated in lightning demos that drew a packed house. Even workshop attendees and early happy hour arrivals crowded in to witness what had been built in just a few hours. Each presentation sparked questions and applause, highlighting just how much can be accomplished when passionate developers collaborate.
The demos showcased an impressive range of completed projects: a Slack Support Bot, an Intelligent Agenda system, an AI Code Edit Loop, and a fully functional Temporal Auction System (backend, frontend) that managed bid submissions with signals, queries, and encryption.
Make sure to check out each project by visiting our dedicated GitHub page!
Angie capped the demos by distributing prizes from a local shop, along with the highly coveted Temporal swag — those Ziggy pins were especially popular!
Workshops: Hands-On Learning Across Languages
While the hackathon teams worked their magic, an annual tradition since the very first Replay was continuing, the workshops. Every year, our Developer Educators deliver our workshops to new and experienced Temporal developers alike. This year the team delivered a new format for the workshops, combining the Temporal 102: Exploring Durable Execution course with the newly released Crafting an Error Handling Strategy course. The courses were in Go, Java, and—for the first time—.NET.
Attendees rolled up their sleeves and worked through practical exercises, gaining real-world skills using Temporal's capabilities.Throughout the day, participants dove deep into the intricacies of building reliable distributed systems, getting hands-on experience that went well beyond theory. The interactive format meant people weren't just listening—they were doing, which is the best way to truly learn any technology.
From explaining how History Replay works to unpacking why determinism is crucial in Temporal applications, attendees explored everything from foundational principles to advanced design patterns. Participants learned not just how to use Temporal, but how to think about building robust, resilient systems.
One of the workshop's highlights was the direct access to Temporal experts. Solutions architects and engineers were on hand throughout the day, answering questions and providing insights. This meant attendees could dig into nuanced topics like error handling, cloud deployments, and worker tuning.
Attendees also spent significant time on practical debugging techniques, teaching participants how to interpret event history and effectively use Temporal's Web UI to interpret the Event History. These skills are invaluable for anyone building Temporal applications.
The workshop raised fascinating questions about more advanced temporal features, signaling a deep hunger in the developer community to push the boundaries of what's possible with distributed systems design. Over 100 attendees attended the workshops, eager to learn about Temporal. And the workshops aren’t just for new attendees! Even those already familiar with Temporal found the workshop enriching—one attendee shared, “More beneficial than expected! I feel I deepened my understanding and am much more confident.”
What’s Next at Replay ‘25: Building on the Momentum
The hackathon and workshops have set the stage perfectly for the rest of Replay '25. With keynotes and technical talks still to come, there’s much more to look forward to. Day one was about building, learning, and sharing—and this is just the beginning. Take a look at our recaps of day two and day three to learn more.
Missed the Hackathon? You still have another chance to contribute to your fellow dev community. Make sure you check out our Code Exchange, take Temporal for a test drive, and stay tuned for more from day two and three of the conference.