Boot-Repair

In some situation, you might loose access to one or several of your operating systems, because of a buggy update, a bootloader problem, or after installing a new OS (e.g. if installing Windows breaks Linux bootloader).

Boot-Repair is a FLOSS graphical tool, generally used from live disc, that will help diagnose and repair many of these problems.

https://sourceforge.net/p/boot-repair/home/Home

It needs to be constantly updated in order to remain compatible with latest versions of Ubuntu (and other distributions), of GRUB, kernels, file systems ...