Pre-built packages for MacOSX, Linux and Windows are available at https://github.com/tomooda/ViennaTalk-doc/releases.
VDMPad is a lightweight WebIDE for VDM-SL shipped with ViennaTalk.
A free VDMPad server is available by courtesy of Kyushu University, Japan. No user registration is required.
VDMTools is a fully featured toolbox for VDM-family with a long history. It has both IDE with GUI and command line tools with features including syntax checkers, type checkers, interpreters, proof obligation generators and code generators. Binary packages (for Mac, Linux and Windows) and documentation (in English and Japanese) are available at fmvdm site, and all source code and documentation are now open-sourced under GPLv3 at github repository.
vdm-mode is an Emacs package for writing VDM specifications using VDM-SL, VDM++ and VDM-RT.