Yep, cwm is maintained by the OpenBSD devs and is part of base, so you don't have to download a package for it. If you want, though, i3 is only a quick dl away.
I used to have a kind of complicated cwm setup, but I got tired of that and just use XFCE now. It runs great.
Ditto, but with JWM instead of XFCE. Minimalist, a rational set of functionalities, click-to-focus-and-raise, plus a CDE-like colorscheme borrowed from AIX.
As for the file manager, I use noice, but I woudn't mind this ported to OpenBSD:
I can’t decide whether the old motif widgets are ugly as sin or not. But for whatever reason, I find the screenshot of that file manager to be salve for my soul. Probably just nostalgia.
I must say though that I’m just as glad Motif has mostly faded into history. It was... a challenging widget set to work with.
Now, I wish something like GNUStep had caught on. Maybe an independent BSD implementation.