First off, esolang is short for esoteric programming language.
Spyrodecimal is an esolang where all the commands are numbers.

Here are all the commands:

0 - Pauses the program for 1/10 second.
1 - Prints the ASCII equivalent of the number in memory.
n - Prints the actual number in memory.
2 - Increases the number in memory.
3 - Decreases the number in memory.
4 - Gets one character of input, and stores it in memory.
5 - Prints a new line.
6 - Generates a random number between 1 and 256 and stores it in memory.
7 - Moves the program reader back for the amount in memory. For example, if 5 is in memory, it will move back 5 spaces.
8 - Erases the memory.
9 - Same as 7, except moves the reader forward instead of backward.
q - Quits the interpreter.
x - quits the program, but not the interpreter.
s - Stores the current memory value into one of six variables (a, b, c, d, e, f). Variables are not affected by 8. Syntax (s<var> example: sa)
r - Recalls the value stored into one of six variables (a, b, c, d, e, f) and stores it in memory. Syntax (r<var> example: ra)

I'm currently working on the interpreter (in C++).
Any ideas are welcome!

Haha nice!

Calc version soon?

Another Project Update!!!
The roles of  7 and 9 have changed:

7 - Ignores everything until the next 7. (Could allow for comments?)
9 - Repeats the command before it once.

And a new command has been added:
x - quits the program, but not the interpreter.
Here's the source:
#include <iostream>
#include <string>
#include <stdlib.h>
#include <windows.h>
using namespace std;
int loopstart = 0;
int main()
{
    cout << "Spyrodecimal Interpreter\nBy Spyro543 -- Type 'q' to exit\n------------------------\n";
    string prgm;
    signed int mem = 0;
    int pos = 0;
    char data;
    bool ignore = false;
    bool repeat = false;
    while (true)
    {
        cout << ">>> ";
        cin >> prgm;
        for (int i=0;i < prgm.length();i++)
        {
            data = prgm[i];
            if (ignore==true)
            {
                if (data=='7')
                {
                    ignore = false;
                }
            }
            else
            {
                switch (data)
                {
                    case '0':
                    Sleep(100);
                    break;
                    case '1':
                    if (prgm[i+1]=='n') cout << mem;
                    else cout << (char)mem;
                    break;
                    case '2':
                    mem++;
                    break;
                    case '3':
                    mem--;
                    break;
                    case '4':
                    char inp;
                    mem = 0;
                    cin >> inp;
                    mem = (int)inp;
                    break;
                    case '5':
                    cout << "\n";
                    break;
                    case '6':
                    mem = rand() % 256 + 1;
                    break;
                    case '7':
                    ignore = true;
                    break;
                    case '8':
                    mem = 0;
                    break;
                    case '9':
                    if (repeat==false)
                    {
                        i--;
                        repeat = true;
                    }
                    else if (repeat==true)
                    {
                        repeat = false;
                    }
                    break;
                    case 'q':
                    return 0;
                    break;
                    case 'n':
                    break;
                    case 'x':
                    goto end;
                    break;
                    default:
                    break;
                }
            }
        }
        end:
        cout << "\nProgram finished.\n";
    }
}
Attached are the source file and executable.

MORE UPDATES!!!

Source:
#include <iostream>
#include <string>
#include <stdlib.h>
#include <windows.h>
using namespace std;
int loopstart = 0;
int main()
{
    cout << "Spyrodecimal Interpreter\nBy Spyro543 -- Type 'q' to exit\n------------------------\n";
    string prgm;
    signed int mem = 0;
    int pos = 0;
    char data;
    signed int a = 0;
    signed int b = 0;
    signed int c = 0;
    signed int d = 0;
    signed int e = 0;
    signed int f = 0;
    char var;
    while (true)
    {
        cout << ">>> ";
        cin >> prgm;
        for (int i=0;i < prgm.length();i++)
        {
            data = prgm[i];
            switch (data)
            {
                case '0':
                Sleep(100);
                break;
                case '1':
                cout << (char)mem;
                break;
                case '2':
                mem++;
                break;
                case '3':
                mem--;
                break;
                case '4':
                char inp;
                mem = 0;
                cin >> inp;
                mem = (int)inp;
                break;
                case '5':
                cout << "\n";
                break;
                case '6':
                mem = rand() % 256 + 1;
                break;
                case '7':
                i -= mem;
                break;
                case '8':
                mem = 0;
                break;
                case '9':
                i += mem;
                break;
                case 'q':
                return 0;
                break;
                case 'n':
                cout << mem;
                break;
                case 'x':
                goto end;
                break;
                case 'r':
                var = prgm[i+1];
                if (var=='a') mem = a;
                else if (var=='b') mem = b;
                else if (var=='c') mem = c;
                else if (var=='d') mem = d;
                else if (var=='e') mem = e;
                else if (var=='f') mem = f;
                break;
                case 's':
                var = prgm[i+1];
                if (var=='a') a = mem;
                else if (var=='b') b = mem;
                else if (var=='c') c = mem;
                else if (var=='d') d = mem;
                else if (var=='e') e = mem;
                else if (var=='f') f = mem;
                break;
                default:
                break;
            }
        }
        end:
        cout << "\nProgram finished.\n";
    }
}Look at the first post, 1n is now n, s and r commands are added, and 7 and 9 are changed.
Download links:
Source: http://anova.57o9.org/junk/spd/spyrodec.cpp
EXE: http://anova.57o9.org/junk/spd/spyrodec.exe

This update takes Spyrodecimal one step further to becoming Turing complete!

Here is my try at a small interpreted language

It has one variable for operations (like your memory, I call it register), 256 labels and 2048 bytes of memory where you can read and write from.


Code:
#include <iostream>
#include <conio.h>
#include <string.h>
#include <string>
#include <windows.h>
#include <time.h>

using namespace std;

int main(void)
{
int memory[2048];
int label[256];
int reg;
int deep;
bool ignore = false;
bool debug = false;
char tmp;
srand((unsigned)time(NULL));
while(true)
{
string program;
cout << endl << ">>>";
cin >> program;
memset(memory,0,2048*sizeof(int));
memset(label,0,256*sizeof(int));
reg = 0;
deep = 0;
for (int i=0; i < program.length(); i++)
{
if(program[i] == 'l')
{
label[program[i+1]] = i+1;
if(debug) cout << "Label " << program[i+1] << " at " << i+1 << endl;
}
}
for (int i=0; i < program.length(); i++)
{
if(ignore && program[i] != ';') continue;
else ignore = false;
if(debug) cout << "op=" << program[i] << ", pos=" << i << ", reg=" << reg << " (" << (char)reg << ")" << endl;
switch(program[i])
{
case 'd':
debug = !debug;
if(debug) cout << "\tdebug=" << debug << endl;
break;
case 'n':
cout << endl;
break;
case 'i':
if(debug) cout << "\tinput ";
cin >> tmp;
reg = tmp;
break;
case 'p':
if(debug) cout << "\tprint " << (char)reg << endl;
else cout << (char)reg;
break;
case 'I':
if(debug) cout << "\tinput ";
cin >> reg;
break;
case 'P':
if(debug) cout << "\tprint " << reg << endl;
else cout << reg;
break;
case 'k':
reg = getch();
break;
case 't':
reg = rand();
if(debug) cout << "\trand=" << (int)reg << endl;
break;
case 'j':
if(debug) cout << "\tlabel=" << program[i+1] << ", pos=" << label[program[i+1]] << endl;
i = label[program[i+1]];
break;
case 's':
memory[program[i+1]] = reg;
i++;
if(debug) cout << "\tmemory(" << program[i] << ")=" << reg << endl;
break;
case 'r':
reg = memory[program[i+1]];
i++;
if(debug) cout << "\tmemory(" << program[i] << ")=" << reg << endl;
break;
case 'S':
memory[memory[program[i+1]]] = reg;
i++;
break;
case 'R':
//cout << program[i+1] << "," << memory[program[i+1]] << "," << memory[memory[program[i+1]]] << endl;
reg = memory[memory[program[i+1]]];
i++;
break;
case '1':
reg++;
break;
case '2':
reg--;
break;
case '+':
if(debug) cout << "\treg=" << reg << ", memory(" << program[i+1] << ")=" << memory[program[i+1]] << ", add=" << reg + memory[program[i+1]] << endl;
reg = reg + memory[program[i+1]];
i++;
break;
case '-':
if(debug) cout << "\treg=" << reg << ", memory(" << program[i+1] << ")=" << memory[program[i+1]] << ", subtract=" << reg - memory[program[i+1]] << endl;
reg = reg - memory[program[i+1]];
i++;
break;
case '/':
if(debug) cout << "\treg=" << reg << ", memory(" << program[i+1] << ")=" << memory[program[i+1]] << ", divide=" << reg / memory[program[i+1]] << endl;
reg = reg / memory[program[i+1]];
i++;
break;
case '*':
if(debug) cout << "\treg=" << reg << ", memory(" << program[i+1] << ")=" << memory[program[i+1]] << ", multiply=" << reg * memory[program[i+1]] << endl;
reg = reg * memory[program[i+1]];
i++;
break;
case 'x':
reg = 0;
break;
case '=':
reg = program[i+1];
i++;
break;
case '?':
if(program[i+1] == '=')
{
if(reg == memory[program[i+2]]) ignore = false;
else ignore = true;
}
else if(program[i+1] == '!')
{
if(reg != memory[program[i+2]]) ignore = false;
else ignore = true;
}
else if(program[i+1] == '>')
{
if(reg > memory[program[i+2]]) ignore = false;
else ignore = true;
}
else if(program[i+1] == '<')
{
if(reg < memory[program[i+2]]) ignore = false;
else ignore = true;
}
if(debug) cout << "\tif reg " << program[i+1] << " memory(" << program[i+2] << ") --> " << ignore << endl;
i += 2;
break;
default:
break;
}
}
}
}
A simple and documented Guess the number:

And a brainfuck interpreter (won't work with nested loops)