Valve are introducing a system into Dota 2 that allows "high-quality" custom games that have "established themselves in the community" to earn their developer money from their work.
You probably can't make money in many of these, but why not peruse our list of PC's best free games while you're here.
Following Dota 2's introduction of custom games back in September's Reborn update, the Custom Game Pass is a new system for supporting and rewarding custom game developers in Dota 2, but it's specifically for those who are committed to building lasting communities around their game modes.
While custom games will remain free to download and play, the option will exist to buy a Custom Game Pass and support the mode's creators, while getting some extra in-game features as a reward for doing so. Custom game developers will receive the same revenue share as any ordinary developer who distributes their work through Steam.
If you're wondering how this differs from Valve's attempt to introduce paid mods via Skyrim, Valve had the following to say: "We learned a lot from the community's feedback on paid mods in Skyrim," said Valve to PCGamer. "While it may appear similar on the surface, the system we're providing for custom games is quite different. There are important details to how it works, and we can walk through some of the community's most important concerns so you can see how they informed our design.
"One of the first concerns the community had was that paid mods meant an end to free content. In this new system, only a small number of custom games will have passes for sale, and those games will continue to be freely downloadable and playable, with Custom Game Passes representing optional additions.
"The community was also worried about quality control and the general 'worthiness' of a mod being paid for. What stopped a mod maker from asking $10 for a minor gameplay tweak? We will be carefully selecting which custom games are able to offer a Custom Game Pass, selecting only games which have already established a sizeable community and are mature enough to offer good value to customers. The community also had concerns about the potential for stolen content in paid mods. The Dota team's curation of the process addresses this, requiring a custom game to be free of copyrighted materials to be considered for a pass."
The first Custom Game Pass will be available for co-op dungeon-crawling mode Roshpit Champions, and will set you back a miniscule $1 for 30 days. While everyone can play Roshpit Champions for free, the Custom Game Pass will enable additional stash and character slots, and offer multiple perks for the duration of the pass.
There's loads more information in a really nice Q&A over on PCGamer, and you should definitely read that.