From what I read OpenAM or OpenSSO fedlets allow an application to act as a service provider, if so I was wondering if full implementation of the product (OpenAM or OpenSSO) is still required to have the SP use ADFS as its IdP. Anyone ever tried it?
Is it correct that Oracle has abandoned development of the OpenSSO solution?
Does anyone know of other open source federation servlets existing?
You do not need the full implementation of OpenAM / OpenSSO to run the fedlets.
Yes - I tried it a long time ago. Yes - it works with ADFS.
No idea if OpenSSO is still being developed but I recall reading that Oracle's OpenSSO support expired in 2014 (for premium support) and expires in 2017 (for extended support).
ForgeRock used OpenSSO as the basis for OpenAM which is still being actively developed.
By fedlet, you mean client-side SAML stack - refer: SAML : SAML connectivity / toolkit and the links therein.