Red Hat holds patents but promises not to enforce them. This means anyone can use the IP without worrying about being sued for infringement. No one else can claim they own the IP because Red Hat already owns it. They also have a clause saying that if Red Hat sells the IP, the buyer needs to uphold the same promise.
The "combined" part seems to be saying you can also develop a system that's partly proprietary, as long as the proprietary parts are simple and not using Red Hat's patents.
If they sell a patent, the buyer must agree to the same promise.
The promise won't protect you if you infringe someone else's IP, even if it's related to one of Red Hat's patents.
Isn't that exactly the same as Facebook's license grant?
Facebook: You can use our software if we can use your patents.
That's my severely over-simplified interpretation. The most significant difference is that Red Hat's promise extends to FOSS in general, though apparently not proprietary software. Facebook's license applies only to specific Facebook FOSS code, but it can be used in proprietary software.
>Our Promise also does not extend to the actions of a party (including past actions) if at any time the party or its affiliate asserts a patent in proceedings against Red Hat (or its affiliate) or any offering of Red Hat (or its affiliate) (including a cross-claim or counterclaim).
So RedHat can hypothetically use all of your software patents and still sue you for infringement based on their patents if you sue them.
RedHat won't sue you over your FOSS project that infringes any of RedHat patents, but your proprietary software is fair game.
Facebook won't sue you for infringement caused by using one of their libraries in your software (FOSS or not), but your independent project (FOSS or not) that infringes any Facebook patent is fair game.
if Facebook [...] files a lawsuit alleging patent infringement against you
in the first instance, and you respond by filing a patent infringement
counterclaim in that lawsuit against that party that is unrelated to the
Software, the license granted hereunder will not terminateIf I read this right, Red Hat promises to not sue anyone for using/transferring FOSS whether or not such an action infringes on Red Hat's patents - they will only use patents to defend against litigation. (IANAL.)