Usually, programs that generate BibTex files (*.bib) can import RIS (Research Information Systems) and thus convert the data from RIS to BIB. There exist also a useful bunch of utilities called Bibutils that can help with RIS to BIB conversion, but may require doing two conversions to reach the goal (RIS to XML and XML to BIB).
Convert Research Information Systems citation to BibTeX document file.
We have found 2 software records in our database eligible for .ris to .bib file format conversion.
Microsoft Windows software - convert ris to bib on Windows
Bibliographic reference and citation management software
Convert from ris file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned ris to bib. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert ris to bib on OS X
A bibliography manager for Mac