These files are the loaders for the EZ5.
There are four main lines presently in existence:
The 2.0 line
The 1.9 line
The 1.86 line
The older lines.

EZ5i users can only use beta 6 of 1.90 and all the 2.0 line.
EZ5 plus users can only use 1.86c and beyond.
EZ5 original and NYE users can use just about anything they can find.

The 2.0 loaders are a total rewrite of the loader bringing loader speed increases.
They now feature all the features that were initially lost in the transition and they are probably better than those they replaced.

The 1.9 line is a beta line but featured some new and interesting tweaks to things. As of this moment 2.0 does everything better than 1.9 but prior to that

1.86c has some features but not as fully developed as the 2.0 line, it does however have the most stable support for the EZ 3 in 1 GBA slot device. While it is considered the stable version of the three it no longer gets backports of fixes.

The most notable use for the even older lines is that they still use a savelist; this is a list of games and their save types that the EZ5 then emulates. This means roms with anti piracy or otherwise in need of a patch can often work with these versions.
They will feature rudimentary cheats and soft reset only.