Here's a non-exhaustive list: Security Scorecards (https://github.com/ossf/scorecard): auto-generated security checks for OSS, Criticality Score (https://github.com/ossf/criticality_score): auto-generated criticality score for OSS, Package Feeds (https://github.com/ossf/package-feeds): watches package registries for updates, malware analysis tools, SLSA (https://github.com/slsa-framework/slsa): proposal for a supply chain integrity framework, Sigstore/Cosign (https://sigstore.dev/): code signing made easy!
We are also investing and exploring different efforts for improving security of critical OSS projects, and making it sustainable! If any of these projects sound interesting, come join us in the OpenSSF Working Groups!
*edited formatting