FX TD (Effects Technical Director)
Effects technical director is a role to direct for generating the effects of natural phenomena, like weather, fog, thunder, tornadoes, etc, and various kinds of destruction as well, unique to the production, and ensure that effects are rendered smoothly for the screen.

Moreover, they incorporate special effects into live-action material, with professional understanding of, art, science, filmmaking and post-production, the FX TD get the finest special effects by programming and successfully convey this to the filmmakers in order for the scenes to function.

TD (Assistant Technical Director)
TD (Assistant technical director) is responsible to solve the technical software problems by creating tools for artists with coding of Python and C++. Some company also name this position as tools developer, pipeline developer, CG developer, software developer for Less-experienced employees. They can organise workflow automatable by script or plugins, instead of repetitions.
Take the experience of John Russell as a DreamWorks Animation’s Technical Director as an example.

For instance, according to John, he created a tool for VFX artist to reframe a perspective camera to an object while allowing to add a minimum padding between the object and the edge of the frame in Maya.

Their works are extremely useful to utilise a variety of industry standard graphical applications, scripting languages and operating systems, and support projects by gathering artist requirements, designing solutions and coding small-scale tools using established employer workflow requirements.
Software Developer
Software developers work closely with technical directors to create more efficient workflow system to fit VFX artists’ requirements. They also create new tools for VFX artists with coding of Python and C++ to suit the need of existing software. This allows objects to be efficiently passed from one VFX phase to the next.
In a research and development stage, they need to figure out how to increase the efficiency of operations. Software developers have to keep their eyes on the latest version of software and technology in their profession. They come up with new approaches to help the artists in the pipeline do their job as quickly and as successfully as possible.
See this article to know more about software developer in Pixar:
https://review.firstround.com/Lessons-from-Pixar-Why-Software-Developers-should-be-Story-Tellers
Pipeline TD (Pipeline Technical Director)
Pipeline TD is a senior role with advanced coding ability in C++ and Python to ensure that a VFX production operates successfully by seeing and resolving issues as they emerge. The different steps of production necessary to add visual effects in a studio are referred to as the VFX pipeline. The pipeline aims to organise each department so that each VFX artist is aware of their responsibilities and a production can stay on schedule.

See this interview of Marieke van Neutigem to know more about pipeline TD in Double Negative:
https://discover.therookies.co/2020/07/18/marieke/
Pipeline TD also ensure that each department has the software tools necessary to accomplish their share of the project to the highest possible quality. They have professional knowledge of how VFX production pipelines operate and the functions of each part performs.
Please also see the article of ProductionBase Community for more details:
Reference:
1.Lidia Martinez’s Blog. (n.d.). All about Technical Directors – Part 1: What is a TD and what makes a good one? [online] Available at: http://blog.lidia-martinez.com/all-about-technical-directors-part-1
2.The Rookies. (n.d.). Markus Kranzler | Rookie Awards 2020. [online] Available at: https://www.therookies.co/contests/groups/rookie-awards-2020/judges/139
3.Alexander Richter TD. (n.d.). Technical Director & Coach | Alexander Richter. [online] Available at: http://www.alexanderrichtertd.com
4.Boshoer, I. (2018). What Pipeline TDs and Engineers Need to Know About Visual Effects Studios. [online] Medium. Available at: https://medium.com/@iboshoer/what-pipeline-tds-and-engineers-need-to-know-about-visual-effects-studios-993c093c8f1d.
5.McMahon, C. (2021). What is a Pipeline TD and how can I become one? [online] ftrack. Available at: https://www.ftrack.com/en/2021/09/what-is-a-pipeline-td.html#what-does-a-pipeline-td-do
6.Spectrum, C.G. (n.d.). FX Technical Director Job Description, Salary, Skills & Software. [online] www.cgspectrum.com. Available at: https://www.cgspectrum.com/career-pathways/fx-technical-director.