If I understand you well, you seek for light/standalone applications. Lxde don't need specific language programs, but if you want to keep it the lightest possible in size as well as in resources, you'll avoid all apps that show obviously that they need lots of depends to work. The list to avoid would be : qt4, java, gnome libs, kde libs. At a certain point you will not be able to avoid a few of them, because of the need for some comfort. Bleachbit, (excellent program to help find and erase unuseful leftover files) needs a few Gnome components (this is an example). Yet, I succeeded in avoiding to install java, but not qt4, as some apps I really want to use need it.
For Treeline, I'm not sure, I tried it once only. Is it to keep tasks to do ? If so, you could give a try to Osmo, which is calendar, adressbook, and task manager at same time... if what you want to do is something else, you may want to explain about it.