You know that LXDE (Lightweight x11 desktop environment) is a very fast desktop environment. It is really extremely fast performing and energy saving desktop environment. So, it support low hardware based computer like older, netbook etc.
Canonical (UBUNTU) thought that if they build a distribution based on LXDE, that will be popular to low end user. So they made a variation named "LUBUNTU". 12 April 2010 was the date of Lubuntu 10.04 beta 2 release date.
What changes were made after beta 1? On mailing list I have found some changes are:
== New stuff since Beta 1 ==Remember that this version is not for regular use. It is still beta now. Use it only for testing purpose.
* Auto-login at install time
* Support encrypted home directory
* Up-to-date lxdm, libfm and pcmanfm2
== Specific Lubuntu changes ==
Lubuntu still contains modifications not available in the official
repository, you can see them in the Lubuntu PPA  :
- New pcmanfm2 and libfm (LP: #523433)
- lubuntu-default-settings with pcmanfm2 support
- Fix for blurry shutdown-icon from elementary-icons (LP: #527345)
- Autologin support in ubiquity (LP: #546445)
- New lxdm