Enabling suveys for external users without login

Step 1.  Enable Communities.

Step 2. Create a public access community.

Step 3.  Go to guest user profile on the community, set full access levels for "Survey, Survey responses, Survey Invitations, Survey Subjects"

Step 3.  Enable Surveys.

Step 4.  Select the default community(created in step 2) for creating public survey invitations.

Step 5.  While sending the survey link, select "Participants Outside Your Company" tab.

Step 6.  Enable "Don't require authentication" check box.

Step 7.  Copy the link to send to external people.