Less features than what? You criticize their products, yet offer no viable alternative. A better question would be "why do you use X instead of Y", where X is a particular 37 signals product, and Y is an alternative that you like better.

Personally, I use Backpack after trying (and not liking) a whole bunch of other solutions for todo lists. I tried

- Outlook

- Pen and paper

- Simple text file

- Command line todo tool (Lifehacker)

- Remember the milk

- Google tasks

and I'm probably forgetting something, it's been a while.

I use Backpack because it's:

- Incredibly simple and intuitive to use

- Offers organization system that makes sense (pages, notes and lists - I use nothing else)

- It's easy and fast to find anything I want

- I can use it everywhere - on my phone, desktop, and the web. I use the web-based client at work and at home, also Mac desktop widget at home, and Satchel on my iPhone. The synching is seamless everywhere.

I'm not going to dignify the "RoR hype" with a response.