Ask HN: What is a good free chat software solution for a website?

On my quick google search, I found several websites, including 1 YC alum, olark.

what i found is mylivechat, purechat, jivosite, olark, zopim, onlinechatcenters.

some offers free with unlimited chats (mylivechat, jivosite, zopim, which somewhat are non US company). Purechat and olark are US company which only offers limited monthly chat (30 for purechat, 20 for olark).

Is there things I should be aware of when comparing different chat solution?

any other chat solution that you would recommend?

Thanks.