TIL that RCTab exists because YouTube showed me nice video on Multi-Winner Rank Choice Voting in Portland's City Council Elections. A quick google lead to RCTab.
RCTab, formerly the RCV Universal Tabulator (RCVUT), is a federally tested open-source software that can tally ranked choice voting (RCV) election results using cast vote records (CVRs) from most voting system vendors. In addition, RCTab can be used to verify RCV results generated by other voting systems. RCTab is the most comprehensive RCV tabulation module to be tested under the Voluntary Voting System Guidelines (VVSG) and the first open-source software to meet VVSG standards.