I'm trying to create a SIP redirect server for LCR routing purpose, I have a basic question here: is opensips is the best solution, and is there other free easier solutions?
Any info on this will be helpful
Yes, it's certainly simple to do in opensips with sl_send_reply or freeswitch with dialplan tools redirect.
If your clients all support SIP 302 redirect that's great. Otherwise you may need to proxy the audio for some legacy clients.