The best replacement for openam is shibboleth.

The best alternatives to openam are rated as following:
★★★★★  shibboleth
★★★★★  opensso
★★★★  cas
★★★★  openidm
★★★★  wso2
★★★  siteminder
★★  opensaml
★  spring security
★  openid
★  openiam

Your alternative for openam is not listed? Suggest!
Speaking about openam, one probably shouldn't forget about opendj.

Other search terms related to openam and their ratings are:
★★★★★ opendj
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Google Trends

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openam
shibboleth
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