HackerBuddy lets you team up (informally) online with another hacker who has skills complementary to yours, e.g. programming vs. design. The two of you can then help each other online with answers to questions on areas that each knows more about.
HackerRank seems to be a way to rank your skills online versus other programmers by solving tests online, and getting scored for your solutions.
HackerRank team and investors.
- Vasudev Ram - Dancing Bison Enterprises