There are various critical appraisal tools available free and online. As already noted, these checklists and worksheets can vary according to the type or study or research that is being appraised.

• A critical appraisal pathway from the National Health Service Scotland

This Critical Appraisal Tools pathway is an interactive site where you can select lists of tools according to the sort of assistance you need, and the study type to be appraised. 

• Understanding Health Research

Understanding Health Research: A Tool for Making Sense of Health Studies "is a tool designed to help people understand and review published health research to decide how dependable and relevant a piece of research is". The Review a Study module guides you through a series of questions about a piece of research you have found, and helps you to evaluate the quality of the research.

• Critical Appraisal Skills Programme (CASP)
  The Critical Appraisal Skills Programme (CASP) is part of Better Value Healthcare, a training organisation led by Professor Sir Muir Gray, and based in Oxford.

CASP is best known for its checklists, a set of eight critical appraisal tools designed to be used when reading research. These eight tools match eight different study or research types.

This highlights that the checklist you use should depend on the type of study you are appraising.

The checklists are free to download, and can be used by anyone under the Creative Commons licence.

• Critical Appraisal Tools (CEBM)
  The Critical Appraisal Tools of the Centre for Evidence-Based Medicine include tools and worksheets for the critical appraisal of different types of medical evidence: systematic reviews, diagnostic studies, prognostic studies, and randomised controlled trials.
   
• Pocket cards (Evidence-Based Medicine Toolbox)
  These pocket cards provide checklists of critical appraisal questions to ask about six types of study: Prognosis; Qualitative Research; Diagnosis; Therapy (single trials); Therapy (systematic reviews); Harm/Etiology. There are also Critical Appraisal Worksheets available in Word doc format.
   
• Lists of Critical Appraisal Tools (ICAHE)
  The Critical Appraisal Tools section of the International Centre for Allied Health Evidence website (at the University of South Australia) includes links to various critical appraisal tools under the headings of the different types of studies.

Special Note: Don't confuse Critical Appraisal Tools with Critically Appraised Topics. Both have the same acronym (CATs).