1. First, I started investigating grub4dos and other boot managers/boot loaders such as syslinux and grub/grub2 in order to boot different payloads from a USB drive. I spent a lot of time on the reboot.pro forum and experimenting with USB drives! There was lots of information, but it was spread out all over the forums. There did not seem to be a good single source of information. Along the way, I added many 'Tutorial' and 'How to' articles to the RMPrepUSB.com website.
2. The first 'eurekamoment' came from a casual post by 'cdob' on reboot.pro. He mentioned the use of the grub4dos partnew command to boot linux ISOs that I had not seen mentioned anywhere before. I tested this method and quickly realised that here was an almost universal method to boot linux ISOs from a USB drive which no-one else seemed to have picked up on because it could only be used on writable media (not CDs/DVDs)! I used the partnew trick with some simple 'auto-menu' grub4dos scripts (which were adapted from grub4dos scripts written by chenall) and Easy2Boot was born! The only downside is that the payload files (ISOs) need to be contiguous - but you can't have everything in life...
3. I then took this a step further by using the partnew command to also mount ext2-formatted files and use them for persistence for some linux ISOs. I added the ability to create these files to RMPrepUSB.
4. People then wanted to be able to directly boot lots of different Windows 7/8/10 Install ISOs from the same USB drive, so I used \AutoUnattend.xml (together with ImDisk to automatically mount the Windows Install ISO as a virtual DVD before Setup started looking for the Install.wim file). Windows PE has a handy feature of automatically scanning Removable media for XML files so there was no need to edit the ISO files.
5. I then investigated methods of installing Windows XP from ISO and found chenall's DPMS grub4dos utility. I improved this (DPMS2) and adapted it to work with the latest Driver pack so that we could install XP to SATA systems straight from an unmodified XP Install ISO. I also worked out a way of adding two virtual F6 floppies (one for firadisk/winvblock and one for the mass storage driver) so that the user did not need to press F6.
6. Next, I wanted to perform UEFI-booting and installs. Using a multiboot UEFI-boot manager/loader turned out to be both horribly complicated and unreliable. One day I had the idea of making an image of a UEFI FAT32 partition and using partnew to replace the whole partition table with a single entry to that FAT32 partition. I tried it and it worked! This also had the advantage that it does not break the secure boot 'chain-of-trust' because no extra bootloader code is involved and it keeps each 'image' completely separate so that they can be simply added or deleted from the E2B USB drive. I am a great believer in the KISS principle! The big disadvantage is that you need to be able to boot in MBR-mode to grub4dos in order to select the partition image in the first place, so I wrote the Switch_E2B.exe utility to 'switch-in' the partition image under Windows first (so not quite as perfect as I would have liked - but hey, it works!).
7. I realised that grub (not grub4dos, but grub2) could boot, via UEFI, directly from an ISO. It required special 'bespoke' grub commands which are specific to each ISO, but it did allow us to boot some linux ISOs that could not be booted using .imgPTN files (because those ISOs did not actually contain UEFI boot files!). This led to the additional grub2 menu system which can be added to E2B.
8. My attention was drawn to the Snappy Driver utility (which can install Windows drivers), Chocolatey (which can install applications) and WSUS Offline Updater (which can install Windows Updates offline), so I devised a way to be able to automatically install Windows drivers + applications + updates without needing to change the Microsoft Windows install ISOs in any way, using SDI_CHOCO scripts.
Along the way I have developed a few 'helper' utilities and scripts to make the USB-booter's (and my!) life easier and also I helped with bug reporting, development and improvements with grub4dos.
Easy2Boot would not have been possible without being able to 'stand on the shoulders of giants' such as chenall, yaya, tinybit, cdob (all grub4dos), Olaf (ImDisk), Marco (WinContig), DavidB (VMUB), many of the contributors on forums such as Wonko/Jaclaz on reboot.pro, plus many other contibutors and developers (sorry if I missed any of you out of the list!).