This is an election counter for the single transferable vote (STV) voting system. STV is a fair way of voting where voters rank their candidates from best to worst. It is similar to instant-runoff voting (IRV), also called alternative vote, and in fact is identical to it where you have elections with only one seat. STV can be thought of as an extension to IRV, allowing for multiple candidates to be elected.
There are multiple different types of STV, and this website uses the Wright system. The author deems this system superior to Pail Lockett's STV election counter, which uses a flawed quota calculation (9 candidates and 2 seats can result in a a quota of 3, meaning 3 candidates can be elected for 2 seats) and does not recalculate the quota when a ballot is exhausted.