https://www.hackerrank.com/domains
This site is a series of well categorized problems. You have the
option of solving the problems in their online compiler and building up a
history of work, but you would need to make an account on their site to do
that. You can always just sort through the problems and solve them
in Visual Studio locally.
http://rosalind.info/problems/locations/
These are bioinformatics themed problems. The site is built
expecting you to solve the problems using Python, but again you could just
look through the problem descriptions and work in Visual Studio with out
tracking your work online.