otherwise, I can't find a difference at all
I love what OpenCollective does but CommunityBridge does more than just funding, "summer of code as a service", security scanning, license scanning etc and is built to deal with a lot of the issues the Linux Foundation ran into scaling projects.
The Linux Foundation is also a non-profit (en.wikipedia.org/wiki/Linux_Founda...)... OpenCollective is a VC funded  organization and not fiscally sustainable due to its patreon style model IMHO 
You can see more ways to fund open source out there by going to oss.fund
 - docs.opencollective.com/help/about...
 - docs.google.com/spreadsheets/d/1uN...
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We strive for transparency and don't collect excess data.