Generally speaking there are no technical restrictions about what you can run on your VPS - almost anything that you can install on a dedicated server or a home PC will run normally on a VPS. 

The below is a quick list of applications and software that you can run on your VPS:

  • web servers: Apache, IIS, and nginx.
  • web applications: WordPress, Magento, MediaWiki, Drupal, Joomla
  • software development platforms: PHP, ASP.NET, Node.js, Ruby on Rails, Python
  • database servers: MySQL, PostgreSQL, Microsoft SQL Server
  • mail servers: qmail, postfix, Exchange
  • groupware and communications: Exchange, Zimbra, Sharepoint.
  • ...and many, many more.