Cluttr is described as 'fast, minimal, and beautiful material design gallery with performance in mind' and is an app in the Photos & Graphics category. There are more than 50 alternatives to Cluttr for a variety of platforms, including Windows, Android, Linux, Mac and Android Tablet. The best alternative is IrfanView. It's not free, so if you're looking for a free alternative, you could try nomacs or Google Photos. Other great apps like Cluttr are ImageGlass (Free, Open Source), XnView MP (Free Personal), FastStone Image Viewer (Free Personal) and XnView (Free Personal).
nomacs is a small, fast image viewer able to handle the most common image formats including RAW images. Additionally it is possible to synchronize multiple viewers. A synchronization of viewers running on the same computer or via LAN is possible.
Google Photos is a photograph and video sharing and storage service by Google. It allows the users to store and share images and videos using the 15 GB free storage space of their Google Account or a Google One subscription.
ImageGlass is a simple picture viewer with which you will be able to display your image collection in a very similar way to the one that Windows provides by default, but with some additional functions.
FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor. It has a nice array of features that include image viewing, management, comparison, red-eye removal, emailing, resizing, cropping and color adjustments.
Simple Gallery is a highly customizable offline gallery. Organize & edit your photos, recover deleted files with the recycle bin, protect & hide files and view a huge variety of different photo & video formats including RAW, SVG and much more.