Yes, Placeit do have a free version with limited free mockup templates that you can use without charge.
They offer free mockup templates for every mockup category in their website but naturally they are not of the best quality.
The quality of the output file is the same as the paid templates but the design quality is not always up to the mark.
Placeit also restricts some high end editing functionalities and options, but that can be expected from any company trying to make a profit.
But the best part is, you can at least check and edit all their pre-made mockup templates for free to know if their service is really useful for your business.
They previously let you download the premium images for free with big watermarks in the past but with the current watermark removal technology they had to stop it.
You can still get the images with watermark if you go a little cheeky but that would be against their terms of service and land you in legal trouble if caught.
So, your best bet is to be happy with the free premade templates they provide or test and edit their premium templates to check if you really need them.
Other option would be look for similar mockup generators like placeit.