Group sequential design has been proposed for a while perhaps since Pocock's paper in 1977. At least for last two decades, the group sequential design and interim analysis have been used in may major clinical trials.
Several years ago, I tried to purchase Cytel's EAST program. But I gave up due to the price and the infrequent use in day-to-day practices.
Now I am pretty happy to know that SAS version 9.2 includes two new procedures for group sequential design. Proc SEQDESIGN allows to calculate the boundaries and Proc SEQTEST allows to perform the tests during the interim analysis whether or not the boundaries have been reached. Proc SEQTEST can also be used to calculate the conditional power (Probability of observing a significant result at full information, given the current data and the specified alternative under the statistical design ) and predictive power.