iconv a GNU utility can help converting text documents back and forth from various encoding schemes. Particularly it is of interest to us, Tamil speaking folks, because it can convert from UTF-8 to TSCII and back.
If you wanted to convert, hello.utf8 from UTF-8 encoding into TSCII you could use it as follows,
$ iconv -f utf-8 -t tscii hello.utf8 > hello.tscii
where in the Linux shell environment you can redirect the output into the TSCII encoded file.
Developers: Someday I hope volunteers will add more historical Tamil encodings, primarily TAM, TAB, and other font-based encoding schemes to the libiconv. Please start development using git repository at GNU sources.