DKey is a simple disambiguation keyboard that allows input using a few keys in much the same was as SMS texting on a mobile phone. It doesn't currently have prediction but that is planned.
Like all my favourite projects this was done to meet a specific user's needs. In this case one of Simon Judge's clients. Simon has been a long term collaborator on Open a11y and was a founder of www.oatsoft.org (and speechmakers before that). Simon wanted to use Tapir but needed a few changes like speech, direct input to another application and keyboard access (well actually synthetic keyboard input from a Grid2 grid that allows scanning switch input).
Tapir looked good as we originally thought (mistakenly, it turns out) that it had prediction as well as disambiguation. So I decided to adapt it and as it is no longer under active development and the changes seemed quite major I basically did a fork for Dkey. As always in hindsight once you know how to do something you can think of a better way and I'd start from scratch next time to avoid a number of problems and lose a lot of unwanted artifacts in the code. Still Tapir is the basic engine and works well. See the Tickets for more detail or more work to be done.
Anyway do try DKey out and let us know what you think. There's more details on the wiki.
Keywords: Accessibility, Alt input, Assistive Technology, keyboard disambiguation, Open Source