c# .net xml xpath xslt regex – gold badge
sql – silver badge
xquery linq tsql – bronze badge

Projects:
WebApi.HealthChecks – offers a WebApi implementation of the health check endpoints for reporting the health of app infrastructure components.
Entity Visualizer – Visual Studio 2017 add-in to display SQL source code generated by Entity Framework
Trie – trie (a.k.a. prefix tree) C# implementation. Has constant-time string prefix lookup.