There are or were a few other OTAs with Roku channels, but none of them have significant broadcast markets other than Comet (I'm excluding shopping and religious OTA networks, many of which have Roku channels):
AMG TV (general entertainment - It used to have a few classic TV shows, but I uninstalled it years ago and I don't know what's on it now)
Biz TV (business)
Comet (already mentioned - it's probably the OTA with the widest reach that has a Roku channel)
DrTV (health)
DW (news)
France 24 (news - now requires a subscription)
Heartland (country music videos and related)
MHz used to stream via Roku for free, but I think it now requires a subscription (drama).
MiCasa (English-language targeting an Hispanic audience - though I think that it stopped broadcasting OTA)
Newsmax TV (news)
Pursuit (outdoor recreation)
Rev'n (automobiles)
Stadium (sports)
Tuff TV (targets men)
WeatherNation (weather)
YouToo America (sports and lifestyle)
2018 and 2017 Roku Ultras, 2017 Roku Streaming Stick+, 2018 Roku Express
Mohu Sky attic antenna
First Generation Dual Tuner Tablo
HP Stream Mini (used as a media server for Plex/PlayOn/iTunes/Web)
Samsung Blu-Ray/DVD
(Roku owner since 2011)