Seeking any sort of funding is something to be very careful of. Even when the developer does provide modding tools (and generally permission to use their IP for mods/expansions of their own game) they might not allow any sort of financial benefit/compensation.
Valve have some policies around with all their SDK stuff. I think this covers most of it: https://partner.steamgames.com/doc/sdk/uploading/distributing_source_engine
Q. Can I sell my Source Engine game on Steam?
A. Yes, but there are a few requirements:
- You will need to complete an additional agreement for distributing a paid Source Engine product on Steam.
- If you are using the RAD tools included with the Source SDK, you will need to contact RAD for information and cost associated with licensing Miles and/or Bink.
- For any Source Engine game that charges money, Havok needs to be paid a licensing fee of $25,000 for the physics engine. You will need to pay this fee up front before making your game available for sale on Steam.
- You can only sell your Source Engine game via Steam unless you get a full Source Engine license.
Q. I’ve got a Source mod that I want to distribute via Steam….
… Source Engine mods must be configured to require ownership of the base game in order to play. …
Q. Can I use Valve IP in my Source Mod?
A. Yes. However, please make it clear on your store pages that your mod is a mod and not created by Valve. Commercial games and mods that include Valve IP such as characters and story-lines need prior approval from Valve.
For free mods not distributed via the Steam store (e.g. earlier in the development and basically just a zip file on one of the (possible non-Valve) community forums), I am not sure, probably another document around somewhere but I suspect largely the same restrictions. It didn't seem to say directly how they consider crowd funding or other monetary sources.
The really problematic ones I can think of is when people want to take game X and make it as a mod for game Y, or completely standalone. Then the developers/publishers of X tend to get unhappy as people can play your thing without buying X in the first place.
Although there are lots of examples of just using some other wider universe with a few well known elements (e.g. how many Star Wars / Star Trek / etc. mods around for various games?), which it doesn't seem much action is taken against, while some IP holders seem to be much more strict and legally it is in the IP holders favour.
Rutin said:
Halo Online which was a fan made mod.
I never really followed Halo. A quick search led me to ElDewrito which seems to still exist. Looks like there was a takedown from Microsoft for the upload of an original Halo Online file (not a mod, there was a closed beta and people redistributed the closed beta files) which were resolved and ElDewrito is still available (although getting the required Halo Online files to play legally sounds like an issue. Reddit has some suggestions, and I guess Microsoft decided to leave it be).