Tetris, without levels, colors and next piece hint. Controls are as follows:
O - move left
P - move right
Q - rotate counter-clockwise
S - rotate clockwise
SPACE - hard drop

Scoring table:
Soft drop: 1 point per row
Hard drop: 2 points per row
single row elimination: 100 points
double row elimination: 300 points
triple row elimination: 600 points
tetris: 1000 points

I recommend running it in fuse emulator. http://fuse-emulator.sourceforge.net/
From the command line, you can type
fuse tetris.tap
to run, but if you start fuse from GUI, you click Media > Tape > Open, 
select tetris.tap. Then you press J in the emulator (types LOAD) and 
Alt+P (types quotation mark) twice and hit ENTER.

Note, that the program starts at line 30, that is the command to start 
it is RUN 30 (press R, type 30 and hit ENTER), if you type it in.

The code:

   10 LET s$(y,x)="#": FOR n=s TO s+2: LET u=CODE y$(n)-98: LET v=CODE x$(n)-98: LET s$(y+i*u+j*v,x+j*u-i*v)="#": NEXT n: FOR n=1 TO 21: PRINT t$(n); OVER 1;AT n,0;s$(n): NEXT n: RETURN 
   20 LET h=t$(y,x)="#": FOR n=s TO s+2: LET u=CODE y$(n)-98: LET v=CODE x$(n)-98: LET h=h OR t$(y+i*u+j*v,x+j*u-i*v)="#": NEXT n: RETURN 
   30 LET x$="acdaacaacabcabcabcccb": LET y$="bbbcbbabbbcbbccbaabcc": DIM t$(21,16): FOR n=1 TO 21: FOR t=1 TO 16: LET t$(n,t)="#"( TO t=1 OR t=16 OR n=21): NEXT t: NEXT n
   40 LET x=8: LET y=3: LET i=INT (3*RND)-1: LET j=(NOT ABS i)*(2*INT (2*RND)-1): LET s=1+3*INT (RND*7): GO SUB 20: IF h THEN RUN 30
   50 PRINT AT 0,0;t-17: DIM s$(21,16): GO SUB 10: LET k$=INKEY$: LET k=(k$="s")-(k$="q"): IF k THEN LET l=k*i: LET i=k*j: LET j=-l: GO SUB 20: IF h THEN LET l=k*j: LET j=k*i: LET i=-l
   60 LET x=x+(k$="p")-(k$="o"): GO SUB 20: IF h THEN LET x=x-(k$="p")+(k$="o")
   70 LET y=y+1: GO SUB 20: IF h THEN LET y=y-1: LET t$(y,x)="#": FOR n=s TO s+2: LET u=CODE y$(n)-98: LET v=CODE x$(n)-98: LET t$(y+i*u+j*v,x+j*u-i*v)="#": NEXT n: GO TO 90
   80 LET t=t+1+(k$=" "): GO TO 50+20*(k$=" ")
   90 LET u=100: LET m=20: FOR n=20 TO 1 STEP -1: LET t$(m)=t$(n): LET v=t$(n)=t$(21): LET t=t+u*v: LET u=u+100*v: LET m=m-NOT v
  100 NEXT n: FOR n=m TO 2 STEP -1: LET t$(n)=t$(1): NEXT n: GO TO 40

Explanation:

Same as with my EXTREME-256 submission. Subroutine 10 has been modified 
to always redraw the entire playing field. This makes it slower, but 
removes the necessity to draw the playing field separately in line 40. 
Since there is no room for initializing the score (in Sinclair BASIC, 
numeric variables do not default to zero, must be initialized), loop 
variable t from initialization is reused for this purpose, but since it 
was left with value 17 in line 30, the score display has 17 subtracted 
in line 50. Initialization itself in line 30 is compacted by two nested 
loops, instead of unrolling the inner one to long literals. This makes 
it slower, but smaller. Scoring is added identically to the EXTREME-256 
submission.