I think mesh gradients are cool, I use them a lot, probably too much.
So I made a simple tool that puts one behind my screenshots.
No watermark, no sign-up, I just paste my screenshot, select my current favorite color palette, I add an unhealthy amount of grain texture, and hit "copy". Lots of aspect ratios available.
I also made a Canvas tool to make more advanced designs with optionally transparent background.
Do check it out and tell me what you think