Satya Nadella, Microsoft announced last 12 of November that a new Visual Studio version was about to be launched with wide opened license allowing free use by individuals and small development groups for either commercial and not commercial uses.
This new version is called Visual Studio Community and arrives at update 4 for Visual Studio 2013. Unlike Visual Studio Express edition Community promises all Visual Studio features for free, specially appreciated are plugin and cross platform support. With Express edition you had no access to the over 5.000 extensions (a.k.a plugins) available for Visual Studio, Community edition changes that and will let you install all plugins you need. Besides Express edition was focused on platform specific development (Web version, PC version, etc). Community edition, following Microsoft new guidelines towards device convergence, unifies that and lets you develop targeting cross-platforms.
With those features, why download Visual Studio Express?, actually I don't know. Some say Community version of Visual Studio will retire Express version, but Microsoft hasn't done so far.
Following its license, you can download for free Visual Studio Community for solo development, either commercial or not, or for group development under 5 individuals if you or your group are not working for an enterprise (which bassically is defined like an organization with 250 PC or 1 million dollars of yearly revenues). If you fall in enterprise category you can only use Community edition for educational and open sources purpuses.