IBM WebSphere Application Server for Developers can be used for free. The installation process is simple after you find the correct URLs to donwload this specific version.

First you need to install the "Installation Manager":
http://www-01.ibm.com/support/docview.wss?uid=swg27025142

After that, go to: File > Preferences, Repositories panel, and add the URL
https://www.ibm.com/software/repositorymanager/V9WASILAN