At the time when this application was released (October 2015) - there are no direct competitor applications in the segment of freeware muti-platform applications designed for probabilistic gas reserves or resources computation using Monte-Carlo method (in terms of supported computation algorithms, units, methods).
Help system for the AGB Gas PB Calc application available here.
Application source code was created to be multi-platform and at present time this application available for the following platforms: Windows OS and Linux OS. Version for Android OS would be released later this year. Quite possible that there would be a version 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.
After project second phase completion author plans to release a commercial version with extended functionality (database support, multiple computation objects, reports). If your company might be interested in purchasing such application or customization of existing application required for the needs of your company - please contact developer using feedback form of support e-mail address available here.