From SpecNext official Wiki
The NextZXOS can read and load these kind of files: bas, tap, nex, z80, sna, snx, dot, o, p
- .z80, .sna and .snx are Spectrum snapshots, more suitable as emulator compatibility than a real format
- .o is a ZX80 snapshot
- .p is a ZX81 snapshot
- .nex is good for a program that takes over the machine
- .dot is good for dot commands and programs that can coexist with BASIC/NextZXOS and can return to BASIC safely (i.e. counterpart to nex)
- .tap is a simple container format that can hold many files, is compatible with emulators and supported by many tools.
- .bas is the native SD-card format for BASIC programs (first 128 bytes of the file form standard +3DOS header).