Current game stage: 1
The concepts of Modlets was introduced in Alpha 17 experimental as a way for modders to make mods that were more compatible with each other.
Rather than changing the vanilla XML files, modlets were installed under the Mods folder, with their changes applied using the xpath system, when the game loads.
[ Legacy Mod Releases ]
Prior to Alpha 17, modders had to edit and re-distribute the vanilla XML files to the players. While this was a straight forward way of distributing mods, it could easily be broken in between alpha releases, even minor ones, as the modder would have to merge the new files with the modded files to find out what has changed.
Also, if a player wanted to further tweak a mod, they would have to edit their files as well, and maintain them in between not only alpha releases, but the modder's own edits and releases as well.
[ Modlet Releases ]
Rather than distribute an edited file or files, a modder can make a modlet that uses the xpath system to apply the changes they want to the game's vanilla files at run time. This allows modders and players to add small modlets to their game, tweaking their game play to their own style. The modlets are designed to only change what they are meant to change, leaving the rest of the files alone.
Since the modlet is installed in the Mods folder, it is not touched when the game updates between alpha releases. Unless the modlet tries to make a change to the vanilla XML files that do not exist anymore, the changes will stay working.
For example, if you install SMX or SimpleUI, and a new alpha release was push from steam, your SMX and SimpleUI mod would still be installed and working. No need for you to re-compare the files and re-merge them.
[ The Tutorials ]
The follow tutorials have been written to help modders and players learn how to deal with the new system.