Borland Turbo C and it's debugger helped me implement my 1st scheduling optimization algorithm, get into production and got me a promotion. Ported it over to IBM mainframe with the help of a colleague which reduced run time to few minutes compared couple of hours on DOS/486

It looked so clunky compared to what my colleagues used in their DEC and SGI (6 processors I think) workstations had, but got the job done