Composure for Mac lets you create photo collages right on your Mac by simply dragging and dropping images into the different frame options. There's tons of frames and aspect ratios to choose from as well as filters, stickers, and more.
To start a collage in Composure just pick a template and the aspect ratio and start dragging and dropping photos from anywhere on your Mac. Supported ratios include 1:1, 4:3, 16:9, and more. After you drop a photo you can resize it, drag it around, and add filters to it. There aren't a ton of editing options but Composure isn't meant to be a full on editing suite, just a way to share collages of existing photos. Filters are another story though. There are tons of them and options to suit pretty much anyone. I actually like Composure's collection of filters better than most other filter apps for both Mac and iOS.
You can also add frames and borders with patterns or solid colors to your collages. Drag the sliders to adjust the thickness of the frame or to control how rounded the edges are. Once you're done adjusting your photos, adding frames, and editing any other aspects, you can choose to share them via Facebook, Twitter, email, SMS, AirDrop, and Flickr. You can also choose to just save it to your Mac.
If you want the ability to create collages from your Mac just as easily as you can with apps like PicFrame for iOS, Composure is not only a great option, it's a free one. There aren't a ton of advanced tools but that's okay. Composure is easy to use and lets you make great looking collages in just seconds.