Quote Originally Posted by xxxxxx;nnnnn
Genie http://support.oticon.ca/...also you must be aware of Genie versus >>Genie2<<
Phonak Target http://fittingsw-objects.phonak.com/....0.1.29364.exe
Phonak iPFG https://www.phonakpro.com/com/en/sup...downloads.html
ReSound Aventa http://www.supportgn.com/resound/sub...es_patches.php
Bernafon Oasis
Starkey Inspire -and- Starkey Patient Database
Connexx6.5.5/SiFit6.10.3 for Siemens/Signia older/legacy
Connexx6.5.5/RexFit6.8.4 for Rexton older/legacy
Connexx8.2.10/SiFit8.2.10 for Siemens/Signia newer/current
Connexx8.2.9/RexFit8.2.1 for Rexton newer/current
UnitronTrueFitCustomer3.4.0 2017.02.01
Hansaton
Widex Compass GPS 2.4, Widex Compass V5 >>Best Effort Search<< may be available as a torrent file... If you are familiar with file-sharing via BitTorrent then post a separate thread asking if anyone has this torrent file, you may get lucky.
I anonymized the above links I found for downloading fitting software. Links may deteriorate over time.

This Easy/Medium/Difficult classification is for how difficult it is to obtain fitting software?
Easy: Oticon-Genie2/Genie, Phonak-Target/iPFG, ReSound-Aventa, Bernafon-Oasis

Sorta-Easy: Starkey-Inspire

Medium: Siemens/Signia-Connexx w/SiFit database, Rexton-Connexx w/RexFit database

Very Difficult: Unitron-Truefit/Unifit, Widex-Compass

Impossible? Costco locked-version of ReSound-Aventa for Kirkland Signature (KS5 and KS6)

Which version of the fitting software? Generally you will want the latest version of the fitting software. The latest version is capable of fitting most of the current hearing aids models including the latest models. However, if you have legacy/older hearing aids then the latest software version may not support your older model.

Some fitting software (Target, Genie/Genie2, Connexx 8, Compass) programs have an update feature that will download and install updates to the fitting software giving you the latest version. Look for it. Also be skeptical about buying Free-Fitting-Software from EBay. You will likely get an older version.

Some vendors switch software platforms, for example;
PhonaK: iPFG software supports older models while the newer Phonak Target software supports newer models.

Oticon: Genie software supports older models while the newer Oticon >>Genie2<< supports newer models (beginning with Opn). Downloading Genie2 gets you both versions but if you want to run the old version instead of running the default new >>Genie2<< version then you need to choose a separate .exe file in order to run the old version. Hint, click this link >>Genie2<<.

Connexx: Connexx Fitting Software has two different parts: 1) The Connexx fitting software 2) The Hearing Instrument/HI database. You need a SiFit HI database for Siemens/Signia HIs. You need a RexFit HI database for Rexton HIs. There are many different versions (old and new) of each of the two parts. Some versions may not run on different Windows OS versions. You will usually find the two pieces you need together in one download. If you want this to work only for Siemens/Signia HIs then install only the version with SiFit HI database. If you want this to work only for Rexton HIs then install only the version with RexFit HI database. If you want it to work for both (Siemens/Signia and Rexton) then install both versions. After installing both you will end up with one Connexx with two HI databases and two commands to run the software. There are other (more obscure) Connexx versions (Hansaton, Electone) not included here.

Widex: COMPASS V5 is for hearing aid families prior to Widex DREAM platform. COMPASS GPS is for programming the DREAM family of hearing aids, which can only be programmed wirelessly through the USB Link or nEARCom.

Note that I intend to update the Original Post/OP as the environment changes.