It is possible to use any SAML2 compliant software in services (SP) and Identity Providers (IdP) that will be added to Haka metadata. Implementor should verify that the product complies with Haka SAML-profile. Shibboleth software is the most used in Haka. Haka is a member in Shibboleth consortium. Wikipedia has a complete list of SAML-products.
Haka operator recommends to use ready made SAML software instead of developing new. Even by help with well matured SAML libraries, developer needs to face complex SAML procedures. Developing SAML software requires thorough familiarity with cryptography.
Shibboleth
Shibboleth is a mature software stack well suited for federated authentication over organisational borders. It is open source software developed in professional lead in Shibboleth consortium and financed by national identity federations mainly in higher education. Software is well documented, has active and wide user base which provides thorough user support in besides of the active developers.
Haka-operator is best prepared to support with Shibboleth-software. With deployers relying on other software stacks Haka support is able to give feedback only on SAML specification level without commenting on the procedures with selected software e.g. in configuration advice.