Freenode runs a bridge. I just tried it out with another channel I manage on Freenode, and it works flawlessly. From a matrix.org (riot.im) account, join this room and the bridge will just do its thing:
#freenode_#ros:matrix.org
They call them “communities” for anyone doing a search.
Communities appear to be a relatively new feature. They do the job, but they kinda suck from a management perspective and from a UI perspective. It’s hard to find the place to add rooms to a community in the UI, rooms are added to communities rather than communities containing rooms, etc. They’ve made the room the top-level entity rather than the community and this has had significant flow-on effects for the management of things.