Telelogic

Telelogic was formed in 1983 inside Televerket and made its name with tools for SDL, the ITU language for describing telecom systems as state machines. Its SDT and later Tau products let engineers simulate models and generate code from them – welcome at customers like Ericsson, where a wrong signal sequence could take down an exchange. It also made the GUI builder TeleUSE.

In 2000 Telelogic bought DOORS, the requirements tool that became standard in aerospace, automotive and defence, where every requirement must trace to a test. IBM acquired the company in 2008 for roughly SEK 7.5 billion and folded it into Rational. DOORS lives on, and nobody who has used it has forgotten it.