https://www.pcgamer.com/epic-wants-everyone-to-use-its-online-services-even-if-they-release-on-steam/

As it already announced, Epic is making its online services available to all developers for free. That includes the cross-platform systems it designed for Fortnite: friends lists, matchmaking, inventory and purchase management, voice chat, analytics, support ticketing, and more. The SDK is available now, Epic announced during its GDC 2019 keynote, and Unity and Unreal integration are coming this year.

There's no catch, says Epic: developers can use its services for any game, using any engine and sold on any store, on Steam or otherwise. For starters, Epic Online Services will support Windows, Mac, and Linux, but console and mobile platform support is on the way.