Colnago’s “BiTitan” is named after its dual down tubes. Yep, you read that right. There were two versions of the BiTitan. The original BiTitan had a typical top tube, whereas the later “Master” BiTitan’s top tube has a diamond cross-sectional shape.
The frame shown in the photographs below is the Master version. The original BiTitan was apparently prone to cracking due to fabrication welding issues. I have read that the issue was improved and was less of an issue (a non-issue?) with the later Master version.
Colnago isn’t known for titanium any more, but back in the day the BiTitan was a sought-after frame. Here is a related CyclingNews quote of Ernesto Colnago regarding the BiTitan.
Oh yes, the Bititan. Well, it was a period where we were refining our expertise in titanium and so we built a bike with a double downtube configuration, so it was more rigid. We built this for Olano, for other riders. Rominger won the Vuelta two times on a Bititan. Olano was a brilliant rider; he came from the track and made a lot of progress at Mapei, where he learned a lot of things from champion riders like Rominger, and Museeuw. That’s where he learned the art of cycling. His win was sensational; he was there with his team-mate Indurain and Pantani. I noticed when he attacked at the end, the cameraman was shooting Olano’s rear wheel with the flat tire. I was just praying that he would make it to the finish line!
The above quote notwithstanding, the BiTitan frames have been criticized for being flexy (laterally). I’ve also heard reports that the frame was not particularly light, which is what you would expect from the dual down tubes. The frame is likely made from 3/2.5 titanium. The BiTitan frames were likely made in either Italy or sourced from Eastern Europe.
Based on the following photographs, you can make your own judgment regarding the aesthetics of the bi-downtube.