Mu4e - Starting with version 0.9.8, mu provides an emacs-based e-mail client which uses mu as its back-end: mu4e.
Invision - Prototyping and collaboration for design teams
Mutt - Mutt is a small but very powerful text-based mail client for Unix operating systems.
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.