uPortal was used by Sakai up until version 1.0, see http://www.uportal.org. Indeed the uPortal Consortium is a member of the Sakai Collaboration. uPortal is an open-standard effort using Java, XML, JSP and J2EE. It is a collaborative development project with the effort shared among several of the JA-SIG member institutions. You may download uPortal and use it on your site at no cost.
The current version of uPortal supports only WSRP consumer interface. The next generation of uPortal (version 3.0) will be fully JSR-168 compliant and will support WSRP with both the producer and consumer interfaces. The most significant change in uPortal v3.0 as compared to v2.3 is that native portlet support will be provided. Currently it is done using an adaptor into uPortal channels. Pluto will be used in both cases. This is further explained on the Web site.