Tools and Resources for Assessing Social Impact (TRASI) is a searchable, expert-reviewed database of over 150 approaches to measuring the impact of social programs and investments. It also features a community portal for nonprofits, grantmakers, and social enterprises to connect with peers and evaluation experts. Launched in 2010, TRASI was developed to address the social sector's need for a knowledge base of tested strategies for evaluation and assessment. TRASI is a project of the Foundation Center, developed in partnership with McKinsey & Co. and with input from experts in the field.
With TRASI you can:

• Browse a listing of over 150 tools and resources for assessing social impact
• Search for tools and resources based on the framework outlined in McKinsey's Learning for Social Impact initiative
• Find ready-to-use tools to conduct a program evaluation
• Learn what leading foundations, nonprofits, and social enterprises are using to measure their impact
• Read the latest foundation-funded reports and case studies
• Connect with a network of peers and experts interested in assessment

Manual from NEF offering a very good introduction to SROI