Hmm, never heard of one, but Google says they can be converted to PDF, so my guess is it's a text document of some sort. Have you tried opening it wit notepad? EDIT: NVM, this link says it's a data file. http://www.fileinfo.net/extension/roi On that site it says Actuate Information Object Designer can open the ROI file.
Hmm, where did you get it from? That could help. Also, it doesn't seem like that Actuate program is out there anymore.
http://www.onixnet.com/actuate/actuate_eReport_Designer_Pro.htm is the application which probably created them. though they could be from a similar application http://www.sharkfinesse.com/productsandservices/sharksalessystem/ Then again... they could be images... http://www.sph.sc.edu/comd/rorden/roiformat/