I'm part of the team at Verlocal, a San Francisco-based start up company. Our product is a platform which allows travelers and locals (or locals and other locals) to connect through sharing experiences. If you are well-versed in a certain skill or are passionate about a certain subject, you can create and share an experience listing. It's a completely free service. If you charge a price for your experience, we simply take a 10% fee.
On the other hand, if you like finding new things to do and make new friends, you can browse experiences to purchase. Here are some of our currently active Seoul experiences that you might want to check out: https://www.verlocal.com/event/modernarchitecturekorea and https://www.verlocal.com/event/achasan. Let us know if you have any questions!