Triplebyte doesn't work as a common app to all YC companies like Work at a Startup. Specific things that we do differently are:

- A background blind technical skills evaluation is our application process in lieu of submitting your resume.

- We don't introduce you to all the companies we work with, only the ones where our data predicts you have a high chance of receiving an offer.

- Companies expedite their own hiring process for Triplebyte candidates skipping technical phone screens/coding challenges.

- Each engineer gets a Talent Manager who offers them career advice, interview and negotiation help and general support throughout the job search process.

- Work with non-YC companies e.g. Apple, Asana and Coursera.

I'd say that Work at a Startup is a good way to get in front of a lot of startups at once and run a breadth first job search. Triplebyte is a good way to run a targeted job search optimizing your offer to interview ratio.