ModulysCS is built around ModulysVst which is a giant step-sequencer/phrase generator in Vst-plugin format. ModulysCS is a portable app for Windows (15MB zip-file) and includes a Csound CSD-editor.
Own presets and instruments can be created by the user. It uses Csound 6.15.0 api for communication and sound generation.
It's totally free without restrictions.
For more info see
raxntrax website
modulyscs website