The OpenIPC project is completely open wherever possible, but it allows the use of various streamers Divinus/Majestic/Mini/Venc/other and various binary drivers and libraries if the chip manufacturer does not provide open source code.
The Divinus streamer is a great alternative to Majestic and it is open and also part of the OpenIPC ecosystem - https://github.com/openipc/divinus
I've found web ui screenshots here: https://openipc.org/web-interface
That said, the actual FPV/camera stuff with openipc is cool too. I definitely would rather pay $50-80 for a 2k 90fps camera/transceiver/receiver system I can hack on in linux than than $300 for a (much better) dji o3 pro. I'm hoping I can get the HDMI out formatted properly to use with my HTC Vive head mounted display instead of having to fork out for something new I can't buy (-11 diopter) prescription lenses for. There's basically no support for glasses wearers in any FPV goggles except the dji ($$$$) stuff.
Dead Comment
Maybe I missed it but it'd be nice to raise the visibility of that a bit more.
https://github.com/openipc/minihttps://github.com/OpenIPC/silicon_research/tree/master/venchttps://github.com/openipc/smolrtsp