MT4 version can be found here.
viewtopic.php?f=38&t=59634&p=89926&hilit=ZeroLagEMA#p89926Formulas:
ZeroLagEMA[i] = Alpha*(2*Price[i]-Price[i-lag])+(1-Alpha)* ZeroLagEMA[i-1], where
Alpha = 2/(Length+1),
Lag = (Length-1)/2.
The indicator was revised and updated