MagicaVoxel is great! Even though the program is not open source, the file format is documented by the creator [0]. For a small game I'm working on I read in the vox files and reconstruct the meshes in-game. I can then create procedurally destructed variations by tweaking the vox data and re-generating the meshes in-game [1]
This is what every software should do. I don't care if software isn't free or open source, but file formats should be documented so that they can be read later or processed by other tools.
I'd go a little further than "documented". MS Office's .docx and .pptx files are "documented" but creating a compatible reader is a major undertaking. I wish people would hold off until there's an existing open source project that can at least decode the files enough to accurately convert the files to another format. Avoid lock-in before has a chance to take root.
This is one of the reasons why I went with Arq for backups - it's a thing I tend to forget about, so if five years down the line the software turns out to no longer exist for whatever reason, I can be confident there's an open source unpacker somewhere.