Cassette 16 Summer Jam

Hello and welcome to Cassette 16 Summer Jam.
This jam is dedicated to good old Zx Spectrum 16K. Rules are as follows:

1. Entry can be loaded by standard way to ZX Spectrum 16K (i.e. by typing LOAD"" command)
2. There is no given topic, all entries are welcomed.
3. Entry should be provided as tap file (it is cassette jam at all). 
4. There is no limit for number of entries per submitter.
5. Entry can be created by a single person or by whole team.
6. By submitting an entry you agree that entry will be released on Cassete 16 compilation by the end of year.

FAQ:

What is exact specification of target machine ?

It is really bare ZX Spectrum 16K without any attached device except tape player and display.

What kind of programming language can I use ?

BASIC and assembler are probably most obvious choices but if you have a Basic compiler, Forth, C compiler than can target 16K model, it is fine to use them.

Is interrupt mode 2 allowed ?

Yes, for purpose of this Jam, consider granted that there is no devil device connected to bus and you can point I register to ROM and exploit one of the few usable vectors at locations xxFF.  If you want to be really nice, either provide Jam version with interrupt table in ROM and final release version with table generated in RAM above 32768. Or you can give user option to choose between 16K and Compatibility mode right after game finishes loading and set up interrupt mode according his choice.

Can I submit a demo ?

Yes. Non-interactive demos are allowed.