I'm a software developer also. I interviewed last year and wore twill, cuffed capris, a linen shirt and boots. I got the shirt at Old Navy, the cuffed capris at Target, and the boots I have had. I still looked professional and not stuffy. I got offered the job with Verizon, but was able to get another one.
In our industry, no, you do not have to be in a suit. A nice solid, button front blouse (silk, linen, or polished cotton), skirt or slacks appropriate for the season (no jeans or khaki's), and low or medium high heels (boots or closed toed shoes). If you are showing leg, do wear light hose. If you are tucking in, wear a nice belt.
Don't overdo it!
Make up should be light for day.
Perfume - if you must, put it on at least 2 hours before you leave the house.
No big hair or big hair accessories.
Keep jewelry simple: studs and a nice chain, one ring per hand, and a watch
I think in most cases, if you go in with an attitude that you don't really need the job, but would love to work for them, you are more relaxed and confident. Even if you do need the job, fake it! Show your confidence and it will all be fine!
Good luck!!!!
Jodi