George,
source code of Cassini is available but is not free - only binaries are. We do sell source code to mostly large companies who don't mind paying premium for the peace of mind.
Having said that, we've successfully maintained six months release cycle, give or take, for a year and a half. So we encourage you to try UltiDev Cassini and send us the feedback - you will probably be surprised by how easy to use it is, and it will also be your chance to have an impact on the product's future.
Best regards,
UltiDev Team.
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