We don't currently expose an API to integrate custom block devices, although it could be possible. We provide an integrated backend based on HTTP byte ranges that can work on any standard compliant HTTP server. See here for more info: https://cheerpx.io/docs/guides/File-System-support#block-dev...

CheerpX is indeed proprietary, but free-to-use for individuals and open source projects. We do want to see the community building on top of our tech. Our Flash product is build on top of CheerpX and the official Flash player plugin that needs to be licensed separately from Harman/Adobe. Java support is provided by a completely different product called CheerpJ, although lots of the ideas and parts of the JIT engines are shared with CheerpX.

At this stage we believe that keeping CheerpX proprietary serves our growth plans the best, this could of course change over time as adoption increases and we build further added-value products on top. On the other hand the WebVM integration is FOSS since it doubles as an extensive sample of what can you build with our technology.