Osso_provider is a project mainly written in PHP, it's free.
OSSO provider feature
OSSO = OpenID Simple Sign On
The following lines of makefile code will download this module's dependencies:
core = "6.x"
; Drupal queue projects[drupal_queue][version] = "1.1"
; KeyAuth projects[keyauth][type] = "module" projects[keyauth][download][type] = "git" projects[keyauth][download][url] = "git://github.com/developmentseed/keyauth.git"
; Open ID Provider projects[openid_provider][type] = "module" projects[openid_provider][download][type] = "cvs" projects[openid_provider][download][module] = "contributions/modules/openid_provider" projects[openid_provider][download][revision] = "DRUPAL-6--1:2010-03-02" ; http://drupal.org/node/621956#comment-2665966 projects[openid_provider][patch][] = "http://drupal.org/files/issues/621956-13_openid_provider_form.patch" ; http://drupal.org/node/810784 projects[openid_provider][patch][] = "http://drupal.org/files/issues/openid_provider-slow_association.patch"
; Open ID Provider SSO projects[openid_provider_sso][type] = "module" projects[openid_provider_sso][download][type] = "git" projects[openid_provider_sso][download][url] = "git://github.com/developmentseed/openid_provider_sso.git"
; PuSH Hub projects[push_hub][type] = "module" projects[push_hub][download][type] = "git" projects[push_hub][download][url] = "git://github.com/developmentseed/push_hub.git"
; XRDS Simple projects[xrds_simple][version] = "1.0"