Onivim is a ‘modern modal editor’, combining fancy interface and language features with vim-style modal editing. What's wrong you ask?
Apart from buggy syntax highlighting, broken scrolling and others, Onivim is proprietary software. It is licensed under a commercial end user agreement license, which prohibits redistribution in both object code and source code formats.
Onivim's core editor logic (bits that belong to vim), have been separated from the interface, into libvim. libvim is licensed under MIT, which means, this ‘extension’ of vim is perfectly in adherence to vim's license text! Outrun Labs are exploiting this loophole (distributing vim as a library) to commercialize Onivim.
Onivim's source code is available on GitHub. They do mention that the source code trickles down to the oni2-mit repository, which (not yet) contains MIT-licensed code, 18 months after each commit to the original repository.
Want to contribute to Onivim? Don't. They make a profit out of your contributions. Currently, Onivim is priced at $19.99, ‘pre-alpha’ pricing which is 80% off the final price! If you are on the lookout for an editor, I would suggest using Vim, charity ware that actually works, and costs $100 lesser.