Cheats:

 In the demo (and perhaps in the full) version works:

 While playing press [/] and then type:

 WIN       - to complete the current stage
 CLOAK     - turns cloaking on/off
 REGENWEAP - regenerates weaponry
 REGENDAM  - regenerates health
 REGENALL  - regenerates everything
 IRONMAN   - invincibility
 IRANGE    - unlimited range of firing
 EYE       - changes view angle