> Multi-tenant (each of my customers gets a fully separate directory, with access to all tenants for our admins)
Yup.
> SAML and OAuth (customers can set up SAML themselves via the SaaS interface, or we set the SP up for them)
You'd have to build an interface using our APIs for this. Not available out of the box, but we do have it in the general roadmap (https://github.com/fusionauth/fusionauth-issues/issues/91 is the tracking issue).
> Rule based group assignment based on SAML attribute evaluation (e.g. assign users to this group if the attribute X = Y)
You could do this with Lambda HTTP Connect (a paid feature) or webhooks (a free feature. https://fusionauth.io/docs/v1/tech/lambdas/#using-lambda-htt... has more
> APIs to manage users, groups, organisations (tenants)
Yup.
> SAML Federations like InCommon...
Hmmm. We have an open issue for supporting this, but I'm not sure what is involved. If it is straight SAML, it should work, but SAML is pretty ... multi-facted so testing would be needed.