In the last few years, Valve has developed multiple new pieces of hardware with software support; the Steam Controller, Steam Link, and HTC Vive. They've also developed and supported a new platform, SteamOS, and rolled out hardware with manufacturing partners. Besides this, the Steam platform has added live-streaming (like twitch), family sharing, big picture mode, the VR UI, and other features. They were also involved in the development of the graphics API Vulkan, which they need for their Linux-based SteamOS to become a better platform.

These are just what I can think of off the top of my head and don't even explicitly involve any games (though they released a collection of 11 small experiences for VR as well).

Interesting thought experiment: Break the sales for DOTA and TF2 into ~$50 increments and compare that number against total sales for the last two GTA's put together. I suspect Valve will beat them at least twice over.