Purple Team

Adversarial Simulation

Uber Metta - Metta is an information security preparedness tool
MITRE CALDERA - Scalable Automated Adversary Emulation Platform
Atomic Red Team - Small and highly portable detection tests based on MITRE's ATT&CK

Threat Modeling

OWASP Threat Dragon - OWASP Threat Dragon is a free, open-source, online threat modelling tool
IriusRisk - Collaborative threat modeling platform for security and DevOps teams
Microsoft's STRIDE - Microsoft's STRIDE is a threat modeling process used to identify potential security threats and vulnerabilities in applications

Metrics

MITRE ATT&CK - MITRE ATT&CK is a globally-accessible knowledge base of adversary tactics and techniques
DeTT&CT - DeTT&CT is a defensive threat and countermeasure matrix based on the MITRE ATT&CK framework
Google's GRR Rapid Response - GRR Rapid Response is an incident response framework focused on remote live forensics

Collaboration

The Purple Team Handbook - A guide to integrating red and blue team activities for improved security
ThreatPlaybook - ThreatPlaybook is an open-source tool for collaborative threat intelligence collection, analysis and dissemination
ThreatModeler - ThreatModeler is a collaborative platform for threat modeling, risk management and compliance

Training & Certification

SANS SEC530: Defensible Security Architecture - A SANS course on how to build and maintain a secure enterprise architecture
CREST Registered Threat Intelligence Analyst - A certification offered by CREST for individuals who are able to carry out threat intelligence projects using open and closed sources of intelligence