I'm currently working on a project that can provide remote desktop assistance like RealVNC. There are many programs already available providing similar services (like these programs). I wrote all code myself.
Can I sell my program or it's not legal because there are already programs providing same features?
In principle it's legal to sell software that acts like VNC.
Better then that: Older versions of the VNC protocol (RFB) are open source, and the protocol details are well documented, which would make it hard for anyone to say "your remote viewing software is infringing on our IP."
It's legal to sell your program if it doesn't infringe any law or anyone else's intellectual property. Examples of things that can get you into trouble:
statutes: Some countries have export laws that forbid you to distribute certain types of encryption without proper export controls.
patents: If you use a design or invention that is under patent protection you could be liable for infringing patent rights.
trademark: If you improperly use a trademarked name you could be subject to damages.
licensing: If you violate a license to which you have agreed you can be sued for damages.
copyright: If you appear to have copied something without license you can be liable for damages.
Just because: If someone wants to sue you, they can.
Since there's no way to guarantee your business won't run into liability from infringement – or from some other failure – people normally conduct business through entities like LLCs that shield them from personal liability. Depending on their concerns and finances, they may also:
Buy liability insurance
Consult professionals like IP lawyers to:
review their business and products in advance to look for and address glaring infringements, and/or
correctly protect their IP using the tools mentioned above.
