Over the years there have been several kinds of archive and tape/disk image formats created. Here is a list of may that you may run across:
.LNX (LYNX, created using various C64 programs including Ultimate Lynx 3. Lynx does not perform any sort of compression, and simply combines multiple files into one single file. It is used as a way to share a collection of related files together for better organization) (although rare to run into, there also is .SDL or Self Dissolving Lynx files, which is a lynx file small enough to be stored fully into the C64 ram, and is made to be so you can LOAD and RUN the SDL to extract to disk without any need for a utility program)
.ARC (Archive, which contains several files put together but using various compression methods to take up less disk space. As these rely on a decent bit of compression, these take longer to create and extract than a LNX file). Various packages exist to create these, including ARC maker and Chris Smeets DOS.(There also are SDA or Self Dissolving Archive (C64 mode only) and SFX or SelF-eXtracting archive. SFX are similar to SDA except they can be loaded in both 64 or 128 mode and take advantage of it’s FAST 2mhz mode)
.LBR (Library, which is similar to LNX as it does not rely on any kind of compression)
.CVT (C64/128 GEOS file which has been converted into a standard CBM file format. Use GeoConvert to convert back and forth)
1!filename,2!filename,3!filename,4!filename (4-pack or more commonly referred to as zip-code disk image. A 1541 disk is read in, using a standard track and sector read, basic compression done, and written as broken up into 4 separate files. This was the normal method to transfer a full disk image online using a modem to a BBS or other user. It should be noted that this only reads basic disk sector data, similar to D64 images and thus only the most basic disk protection can be handled).
1!!filename, 2!!, etc, 6!! (similar to the more common 4-pack zipcode, except requiring 6 files, each with two ! marks. A six-pack zip-code reads a disk GCR data, and thus is able to read some more advanced disk protection data (however it still is unable to handle more advanced protections). It also does not perform any disk compression on the data.
.WRA (Wraptor, a file archive program that uses a fairly high compression. Wraptor was only included to subscribers to the LoadStar disk magazine, and as such, is fairly uncommon to run across)
For Zip-Code files, it’s recommended to use Zip-Code II by Dark Star software. For dissolving the other C64 archives, Omega-Q II has support to decompress them (except for Wraptor)
Additionally, when C64 emulators came about, there were other disk/tape images:
D64 (A simple track/sector disk image of a 1541 disk. Just like 4-pack Zip-code, only the simplest of copy protections can be handled by this)
G64 (A GCR disk image of a 1541 disk. This is able to handle various detailed disk data, including weak bits, track alignment, and as such is possible to store a disk with copy protection (if read in correctly)
T64 (A generic tape wrapped file, which can only handle storing standard files, but act as if it’s loading from a tape)
TAP (This is a full tape image, and is able to store detailed tape signals, which includes tapes with uncommon data or copy protection)
There also are the following disk images:
D71 – (1571 image)
D81 – (1581 image)
D2M – (CMD FD-2000 image)
D4M – (CMD FD-4000 image)
DND (CMD Hard drive image)
DNP (CMD Partition image)
For Windows users, there is the program DirMaster by Style which supports pretty much every type listed here.