Zaru Go (ザル碁) is a rule set propounded by Iehiro? here.
Rules of Zaru Go
When a player passes he gives the opponent one stone as a captive.
End of game
The game ends with two consecutive passes.
Each player's score is the number of captives he has.
Other rules are as in regular go.
Bill: Iehiro develops zarugo step by step, starting from atari go, which he calls pon go. He points out that Zaru Go is equivalent to stone counting if White must make the last pass, à la AGA rules.
RobertJasiek: Did Iehiro develop this independently? Who was first - he or I with PrisonerCountingForStoneScoring?
Bill: It appears that he came up with Zaru Go before Dec. 24, 2000, which is the date for the counter on his web page.
RobertJasiek: Zaro Go seems to allow pass fights, so we created different things. His is a Go variant - not Go. The idea of scoring / counting only pass stones was developed independently by either of us, it seems - but for apparently different purposes.
Sandra: I don't really see a difference. He also has white passing last.
See also Zaru Go Problem 1.