This is an inputfield module integrating Trumbowyg WYSIWYG editor into ProcessWire, quickly hacked together after some discussion at the Redactor thread. Trumbowyg is a light-weight alternative to more feature-rich editors, such as CKEditor or TinyMCE.
Both this module and Trumbowyg itself are still in alpha state.
Customisation options include only a subset of what Trumbowyg provides, more will be added in the near future. Also, link and image features as seen in other RTE modules (TinyMCE and CKEditor) are not implemented yet.
The module is available at https://github.com/teppokoivula/InputfieldTrumbowyg.