00Text is an open source text editor with an old mobile phone like keyboard for the 3DS.
Installation
Available as a 3DSX/SMDH.
Copy the 00Text folder containing .3dsx and .smdh to the 3ds folder in your SD card. Run it with homebre launcher.
User guide
Use the different buttons to select the letters.
Controls
Up - A, B, C
Right - D, E, F
Down - G, H, I
Left - J, K, L
X - M, N, O
A - P, Q, R, S
B - T, U, V
Y - W, X, Y, Z
Select - Debug
Start - Exit
L - Print selected letter
R - Delete
ZL - Space
ZR - Print everything written