I want to use Across / OmegaT in order to translate TTX files.
You can translate some types of TTX files with OmegaT directly (this only works if either you or your client actually has TagEditor, because the files have to be "prepared" for OmegaT in a way that is not mentioned in the user manual). You can translate many types of TTX files if you install the Okapi filter plugin in OmegaT.
I have come across some forums / articles which state that TTXpress can be used to convert TTX files to other formats which are compatible with Across / OmegaT.
TTXpress converts the TTX file into an RTF file, and back. OmegaT can't handle RTF files. Besides, it converts it into "uncleaned RTF" files, which OmegaT really, really can't handle without much hacking and hoping. And it will only convert the TTX file if it is fully translated or pre-translated.
[One thing I can say in TTXpress' favour is that it doesn't use the target text of the TTX file as both the source and target text in the RTF file, but correctly uses the TTX's actual source text as the source text in the RTF file... so if you know that your TTX file is fully translated, and you have a CAT tool that supports "uncleaned RTF" files, then TTXpress looks like a viable option.]
However I couldn't get any working links to download the tool.
I confirm that the link at the bottom of the first post of this thread works, and although Windows 7 complained about incompatability, I was able to install it and use it. For me, the toolbar wasn't added to MS Word automatically -- I had to add it manually using Tools > Templates & Add-Ins > Add, but thankfully the DOT file was in the default list when I did.
I don't use Swordfish but I can confirm that the creator of Swordfish confirmed that Swordfish does handle TTX files, even if they're fully untranslated, partially segmented, partially translated or fully pre-translated, although Swordfish's segmentation settings will segment the text slightly differently, which means that you'll get fewer matches from a Trados TM, if you use one, but otherwise won't affect compatability of the TTX file.
[Edited at 2015-01-12 07:16 GMT]