Jules Testard
Co-founder and CEO of GCast
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| Current role | Co-founder and CEO, GCast |
| Location | Paris, France |
| Education | BSc McGill University; MSc UC San Diego |
Jules Testard is a French software engineer and entrepreneur based in Paris. He is co-founder and CEO of GCast, a mobile game casting startup that streams a phone's game display to televisions and other screens over WiFi. He previously co-founded Jam.gg — originally Piepacker — a Y Combinator-backed cloud gaming platform that raised $15 million in total funding and grew to 8 million registered users before winding down.13 Before founding companies, Testard was on the founding team for AWS Glue at Amazon, worked on Docker Enterprise Edition's Kubernetes integration, and built high-frequency ad trading systems at MadHive.1
Testard co-founded GCast in 2025 with Filippo Scognamiglio, his former colleague from Jam.gg, who serves as CTO. GCast captures the rendered output of whatever mobile game is running on a user's phone and streams it over a local WiFi network to a television, streaming dongle, or browser tab — keeping all game processing on the device rather than offloading it to cloud servers.2 The app reports a display latency of 16 milliseconds and supports receivers including Chromecast, Amazon Fire TV, Apple TV, Samsung and LG smart TVs, and desktop browsers.2
GCast launched in public beta on the App Store and Google Play in 2026 with Testard as CEO.1 The company joined the inaugural Canopy Spring 2026 cohort at Founders, Inc. at Fort Mason in San Francisco.1
Testard co-founded Piepacker in 2020 alongside Benjamin Devienne, who served as CEO. Piepacker launched in public beta in March 2020 as a browser-based platform for playing licensed multiplayer retro and party games without downloading software, using what the company described as a patented technology that reduced internet bandwidth requirements by a factor of 15.3 The company was accepted into Y Combinator's Summer 2020 batch.3
By October 2021, the platform had grown to nearly half a million beta users with a catalogue of more than 80 licensed games from publishers including Codemasters, Interplay, Team17, and Data East.4 That month, Piepacker raised a $12 million Series A led by LEGO Ventures, with participation from Makers Fund and V13 Invest — a fund affiliated with FDJ and managed by Serena — bringing total funds raised to $15 million.4 In 2022, the company rebranded from Piepacker to Jam.gg as it expanded its library onto mobile.5
After a strategic pivot in 2023, the entity split into two separately operating companies — Jam and Onibi — with Y Combinator on both cap tables.3 Testard took over as CEO following the pivot, signing $1.3 million in B2B contracts.1 Over his five years with the company he wrote 30 percent of the codebase.1 The platform reached 8 million registered users before winding down.1
Before co-founding Piepacker, Testard was on the founding team for AWS Glue, Amazon's serverless data integration service, where he built the metadata crawler backend.1 He then worked on Docker Enterprise Edition's Kubernetes integration at Docker, Inc.1 His third pre-founder role was at MadHive, a programmatic advertising company, where he built a high-frequency ad trading system.1
Testard has described his interests as distributed systems, hacking things together quickly, surfing, and gaming.3
Testard holds a Bachelor of Science in Computer Science from McGill University and a Master of Science from the University of California, San Diego.1 His public GitHub repositories include course projects from UCSD's operating systems and advanced compilers graduate sequences, as well as a McGill undergraduate research project on graph database representations optimized for large-scale nearest-neighbor search on disk.6