I have tried most of Note& GDT tools. Comparatively,MemPad is an excellent one.
Pro’s: Free; Portable; Lower RAM usage even than Winpad; Light (160KB); Tree structure,good for simple GTD and diary.
Con’s: No sync with Mobile and Cloud.
Below is the offical description and download link:
MemPad is a plain text outliner and note taking program with a structured index. All pages are stored in a single file. User interface available in 16 languages. Unicode.
The program offers standard editing functions including cut, copy, paste, undo, date/time insert, drag&drop, and supports Web links as well as network and local file or folder links (full path not required) and internal page links. Environment variables can be used in file links to run programs, for example.
The index structure can be modified by buttons, context menu or hotkeys.
Cut&paste functions and quick node moving.
MemPad always saves data without prompting (when closing Mempad or opening another file).
Optional auto save (every 4 minutes).
Automatic backup (can be disabled by option); restore last backup, reload file.
Search through all pages or within a node; continue searching forwards or backwards; Replace.
Sort nodes (siblings) ascending/descending.
Word wrap mode, Read-only file handling, page locking (global or individual);
memory stack (pages, text positions) for browser type back/forw. jumping
Options include: Selectable font, Background color, Minimize to System Tray, Hotkey, Always on top, ESC shortcut to quit or minimize.
Popup menus with user defined words or expressions to insert, optionally with date and time tokens.
Configurable Web look up (dictionary etc.) through context menu.
Mini Launcher (through Tool button, menu, System Tray)
Diary support with year/month/day index structure. Go to (or create) today’s page with a key stroke.
Export page, node or all to a file or directly to another program; import functions.
Insert text file as page.
Password protected encryption, optionally in Win98 compatible mode.
MemPad operates in file environments (by extension and/or directory), each with its own INI file. No Registry entries. File/Open menu within a chosen file environment; optional “New Window”.
Help is provided as MemPad file (in English, see image).