I will look at two bits of software that are for free and every home 3D printing uses should get.
MiniMagics (from Materialise) and NettFab Free (from NettFab) also known as NettFab Basic.
First of all who can use them.
For Minimagics you are limited to using certain types of Widows OS and this is a limiting factor those using Linux, Mac & Windows 98, Windows 2000 or Windows 8
NettFab Basic can run on Windows XP/ 7 / 8, Linux & Mac OS X
Why I use them?
I can always recreate STL files from the CAD data that I keep archived but for some work I also keep the original STL file at the setting I used. So that this does not take up too much room on hard drives compressing them in a form that I can easily view them whenever I want to is always best done using the viewer format.
Which one is the most compressed?
See added file "size stl" and it show 6 examples of typical moulding wheels that have been compressed using Minimagics (MGX) and NettFab Free (NCM). I consider the winner of this to be Minimagics as they have some special algorithms that checks if two facets are planar with each other then a four sided facet uses less description than two triangular facet information, I can only assume this but it would seen logical.
Why 3D printing hubs do not use these types of compression file formats I do not know but they would be quicker to upload and I find that I do not waste so much email space send compressed STL files.
The last thing that I should comment on is that NettFab does allow you to reposition CAD file orientation prior to sending them to a service bureau so that you if you consider what features you want being built in the best orientation then you could do.
It also allows many more import files to view like slice files and AMF files.
If you want more info. then do ask.
cae11c56 this person in the engineers on GrabCAD does not exist????
But to answer his suggestion of Tinkercad this is an online site and only a 3D CAD modelling tool.
The features on the site does not mention editing STL files to correct them.
If you are dealing with lots of STL files then I would suggest using either Minimagics or NettFab basic as both can compress your files for easy storage on your hard drive or memory stick. Minimagics has better compression. But NettFab can correct errors.
As for online repositories I did this once and and they went out of business, so where did my models end up? and do you know who else is looking at them, if Hackers can get into Yahoo!
I would rather look after my own security and IP protection.