At the time when this application was published (May 2015) - there is no direct competitor applications in the segment of muti-platform applications designed for the oil and gas reserves computation (in terms of supported computation algorithms, units, methods).
Application source code was created to be multi-platform and at present time this application available for the following platforms: Android, Linux and Windows OS. Quite possible, that there would be a version released for MacOS as well. Most likely distribution conditions for all of they would stay the same - as freeware application license. Release of iOS version also possible - but not planned because it's required significant financial investments - and as a result not currently planned until external investment would be available.