Yes, people from outside the United States are eligible to participate.
TriangleSCI welcomes applicants from outside the US, and believes that their contributions are especially helpful in providing diverse perspectives.
If a proposal/team with non-US participants is selected to attend, TriangleSCI can cover the travel expenses for the non-US participants just like it would for participants coming from the US.
Participants from outside the United States will need to sort out their own visa or other permissions needed to enter the US. TriangleSCI can provide a letter of invitation that may help that process, but they will need to be prepared to obtain the appropriate entry/visit permissions on their own. There is also some additional paperwork that will be needed in order to process travel expense reimbursements to non-US citizens, but this has not been a problem for participants from overseas who attended in past years.