mac and pc client:
http://cyberduck.ch/

1. download client, install
2. File> Open Connection> "S3" from the type list
3. GRM s3 credentials. you have to put both of these keys in, there are labels for the boxes to put them in
access key: AKIAJSXQJHPGZIPOLLGQ
secret access key: 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
4. click on "more options" add /grassrootsmapping as the path
5. connect