The BitApps team has created a free online testing platform. You can use it to test their plugins, but now they are opening it up so you can use it to test other plugins and themes. There is a checkbox for installing their plugins on the test site.
You can use the sites for 7 days before they are reset. It looks like they may intend to create a platform like InstaWP or TasteWP. You need to provide your email address to log in and that signs you up to their newsletter. I would not install or add any sensitive info on the test sites as there is no password.
They are currently gathering feedback from users.