Imaginario is described as 'open-source, cross-platform photo manager for the desktop with a version optimized for mobile devices running Ubuntu. It features built-in filterable search, great tagging with hierarchical categories and automatic face-tagging and more'. There are more than 50 alternatives to Imaginario for a variety of platforms, including Windows, Android, Mac, Linux and iPhone. The best alternative is IrfanView. It's not free, so if you're looking for a free alternative, you could try nomacs or ImageGlass. Other great apps like Imaginario are Google Photos (Freemium), XnView MP (Free Personal), digiKam (Free, Open Source) and FastStone Image Viewer (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.
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.
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.
digiKam is an advanced digital photo management application which makes importing and organizing digital photos a "snap". The photos are organized in albums which can be sorted chronologically, by folder layout or by custom collections.
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.