Like obs and playstv. I hate that there's no automatic recording in obs and playtv creates huge files. It must be free and last I heard Fraps was paid with lousy trial.

If you're using an NVIDIA card then I highly recommend ShadowPlay which comes with NVIDIA Experience. More info here.

Unfortunately, I don't.

Don't use Fraps. It's totally deprecated.

Get MSI Afterburner instead. Despite its name (it was developed by MSI) it has no manufacturer lock and can be used on any graphic card. And it's free on top.

It's way better than Fraps or Shadowplay, works on all common GPUs, supports hardware encoding with h.264 on Nvidia, AMD and Intel GPUs that support that feature (quality and bitrate are configurable), supports recording in different framerates and resolutions than you are playing, supports sound recording in 5.1 if you want to do so (or downmixes to stereo if you don't) and supports automatic recording.

You can for example tell Afterburner to cap the game at 60fps if the fps fluctuate too wildly and let it record in 30 fps which is exactly half of it and record in 720p while you are playing in 1080p using hardware h.264 compression for a very smooth good looking and small video. If the resulting video has too many compression artifacts for your taste simply up the bitrate of the video until you hardly see them any more. That does make the video bigger of course.

And these are just the recording options. Afterburner is also an overclocking and statistics tool. I suggest you don't mess with the overclocking settings unless you know exactly what you are doing. But the statistics can be very useful. Stuff like FPS, CPU/GPU usage, temperature, voltage, power consumption, clock rate, fan speed, etc. can be tracked and displayed in an overlay on your game screen. Very nice if you are interested in that kind of stuff or if you want to troubleshoot problems. For example if you have intermittent and difficult to reproduce problems during playing some games and want to know if that is due to GPU or CPU overheating you can easily find that out with Afterburner. The overlay can be configured to show up (or not show up) on screenshots and videos and it can also be switched on and off with a hotkey.

Though because of all the options the program is obviously a bit more complex than Shadowplay or PlaysTV. If you are fine with OBS however that should not be a problem as it's nowhere near the complexity of OBS. And once you have configured Afterburner the way you want using it is very simple and straightforward.

I'm honestly surprised that this program is only known by very few people.

What do you mean with "automatic recording" exactly?
It should start on its own whenever you open a game?

It should start like playstv.

Follow Geralt_of_Rivia advice and try MSI Afterburner, it's very good. It comes and works together with Rivatuner Statistics Server (RTSS).