How many valid programs can you write?
APL (Dyalog Unicode) version 16.0, 8384 programs

⍝ empty program
&#32;⍝ single space
&#9;⍝ single tab
0
1
2
3
4
5
6
7
8
9
+
-
×
÷
⌈
⌊
*
⍟
|
!
○
~
∨
∧
⍱
⍲
&lt;
≤
=
≥
&gt;
≠
≡
≢
⍴
,
⍪
⍳
↑
↓
?
⍒
⍋
⍉
⌽
⊖
∊
⊥
⊤
⍎
⍕
⌹
⊂
⊃
∪
∩
⍷
⌷
→
⎕
1 2 3           ⍝ input for above program
⍞
Hello, World!   ⍝ input for above program
/
⌿
\
⍀
¨
&amp;
⍨
⌶
#
⊆
⊣
⊢
⌸
⍸
⍝
⋄
L:
⍬
{}
⍝ just a newline
⍝ this line belong with the previous one

Try it online! (except for two which cannot run on TIO's version 15.0)
Explanations:
Most of the programs just print their content. Exceptions are:

The four whitespace ones do nothing.
→ terminates
⎕ asks for evaluated input
⍞ asks for character input
⍝ is a comment
⋄ is a statement separator (i.e. two statements that each do nothing)
⍬ prints an empty numeric list (i.e. just a newline)