Most interviews designed for hiring coders are flawed. Puzzles and other parlor tricks (like asking "Why are manhole covers round?") suck at judging your candidate's coding abilities. We should be judging coders by asking them to do what they do best - code.
Moreover many coders are introverts and non-glib. They don't do well when confronted with questions demanding quick answers. Your 20 minute time slot is not usually the right time for them to respond.
The only right way to interview a candidate is to work with them on a project. Ideally for several days. But there is a catch. You cannot give such attention to everyone applying for your job. Fortunately for you there is a solution.
Most of the candidates who apply for your job are either not serious or are non-programming programmers. They are prepared to talk about "Why are man hole covers round" and "that cool algorithm that google uses on their auto-driving cars". Ask them to build the simplest application and they will fail. Filter them out and you get access to the good ones that you *can give a lot of time.
So that's what cull.io is designed to do. To give you a way to filter out non-serious, non-coding coders and only let potentially-awesome candidates apply for your Job. The idea is simple. You create a challenge requiring the candidates to build a web app that does 'something'. Candidates write a webservice on their localhost to solve the challenge. Once they solve it, we collect their resume and send you a mail. The following are some advantages cull.io provides over other services like topcoder and interviewstreet:
1. Since candidates write a web service on local host they can chose any IDE, language, libraries or framework. No restrictions. In fact many a times what tools they choose tells you a lot about them
2. You don't have to limit the questions to be overly algorithmic. It can more real-world stuff like "parse this xml", "scrape this page". And see what tools they employ
3. But if you need, it can be overly algorithmic too. Things like "Break this captcha". Again since cull.io does not impose any restriction on the libraries it'll be interesting to see how candidates solve these.