I've built web apps in Sinatra and Rails that have received a significant amount of traffic and made me some money. I love databases and have significant experience with Postgres, DynamoDB, and Redis. Although it's not directly dev-related, I've done a fair bit of SEO and am pretty good at it.
Haven't done much C# desktop apps (and can't say that I want to), but I wrote a significant console app in C# and have a strong grasp of the language.
Other stuff I should mention: I love hosting things on Heroku and using their hosted Postgres service and would be happy to talk about either of those. I also love AWS and their managed services (such as DynamoDB) in particular.