@simon @wikipedia @seav @edward A quick scan shows Wikipedia articles on occam, Ten15 and OSF's ANDF (latter two are the same thing), BCPL, Simula etc.. All were influential (not sure about Ten15), but had a small number of users mainly decades ago: in the main they deserve articles because they provide important historical context for later developments. This is not only true of Potlatch (for the conception of iD by @richardf), but it also had massively more users.
@SK53 @wikipedia @seav @edward @richardf my guesstimate would be ~half a million users, which is a lot more than a -lot- of other "specialist" software.