CleverPDF is a comprehensive PDF web app, which offers 27 PDF tools online for free. It helps users convert PDF to Office, iWork, images and more. Users can also compress PDF, merge or split PDF, rotate PDF, add watermark or numbers to PDF and more. It's completely free, no sign-up is required.
XnView MP stands for Multi Platform = it is available for Windows, Linux and MacOS. It is a continuation of the older XnView Classic. In my opinion it is a great alternative to Windows photos app or any Linux image viewer that comes preinstalled. I even think it is an alternative to IrfanView. It is really fast and simple to use, supports more than 500 image formats, has built in folder browser, image converter, editor... AND MORE!
PDF Joiner - This online tool allows you to join several PDF documents into a single file, free of charge.
IrfanView - IrfanView ... one of the most popular viewers worldwide.
DocuPUB - DocuPUB is an online file converter, file merger, file compressor, and file resizing tool.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
PDFChef Merge PDF - PDFChef Merge PDF is an online tool that allows you to merge multiple PDf files into one quickly and securely.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.