VSDC is as good as many paid video editing programs i've used. i don't find it quite as intuitive as the old sony days of vegas, but it's good, and it's easy to find how-tos for it. one feature i needed was on the pro version, and for $20, it's a steal. btw, i believe you get 2 installs for that $20, or at least that used to be the case.
i don't think it's open source, but it's easy peasy. the only easier might be boilsoft video joiner, but VSDC will let you cross fade between your clips.