FSS ePub Reader is a simple viewer for ePub files, a commonly-used ebook format.
The program installs without issue. There's no adware, and although you're offered the chance to download several of the developer's other applications, those options are turned off by default.
Launching FSS ePub Reader displays a very simple interface, just one window, a couple of panes and a tiny toolbar. Drag and drop your target ePub file onto the program - or use the Open button - and you're ready to read.
The viewer is simple, but has the core basics. Chapters are listed on the left, text and graphics appears on the right, and you can scroll up and down using the mouse wheel, arrow buttons and the other keys you'd expect (PgUp, PgDn, Home, End).
You're able to zoom in or out by clicking toolbar buttons, or holding down Ctrl and spinning the mouse wheel.
Switching to "Night Mode" displays your pages using white text on a black background, maybe reducing glare.
The only surprising extra here is a "Convert" tool, which can save your current document in PDF, text or HTML. This didn't work well for us - our PDFs regularly had line breaks in the wrong place - but some documents were converted successfully, so it's worth a try.