Freer monads (or, for emphasis, free-er) are free monads on an endofunctor which is not necessarily strong.
They are used to construct models of effectful computation within functional languages.
Kiselyov, Oleg, and Hiromi Ishii. 2015. ‘Freer Monads, More Extensible Effects’. In Proceedings of the 2015 ACM SIGPLAN Symposium on Haskell, 94–105. ACM. https://doi.org/10.1145/2804302.2804319. [pdf]
@inproceedings{kiselyov_2015,
title = {Freer monads, more extensible effects},
doi = {10.1145/2804302.2804319},
booktitle = {Proceedings of the 2015 {ACM} {SIGPLAN} {Symposium} on {Haskell}},
publisher = {ACM},
author = {Kiselyov, Oleg and Ishii, Hiromi},
month = aug,
year = {2015},
pages = {94--105}
}