I have some utilities I've made in order to work with binary files, tape sounds and assembler. Also I will link here a set of great utilities -not mines- I've used and I found great.

My Own Utilities

All these are MS-DOS stuff intended to get easy the conversion of tape images to data and reverse.

WMSXF2W	Win Msx File to Wav: It's an utility to create playable .WAV files from binary .BIN files, ascii files, and tokenized files. It's great to load on the old MSX the games you have in the PC for the emulator. Simply set the file that you want to convert and press Start to do the job.
MSXF2W	Msx File to Wav Command Line: It's the command line utility, same as above. An example: MSXF2W LINE4.BIN LINE4.WAV -2 will create a file LINE4.WAV that is the tape sound image of LINE4.BIN at 2400.
MSXR2B	Msx ROM file to Binaries : It's an utility to create binary files from ROM ones (up to 32K). It means that you can execute roms by loading binaries with BLOAD"name",R command. With this and the MSXF2W, you can convert and load into your old MSX1 only with tape connectors, these classic games that you can only run now on the PC emulators.
MSXTAP	Msx Tape loader : Originally it's a program made by Zoran Majcenic for linux in order to get all data from the sound blaster or a RAW sound file in the MSX tape format and convert them to binary file. I have no linux and I needed the utility, so I modified the code and compile it to get an MS-DOS converter (only for files, not soundblaster) and it worked fine !. Here you have it. Just type MSXTAP MYFILE.WAV and It will survey the file in order to discover any MSX binary file (NOTE: only binary, not CLOAD or LOAD formats), and it will create the found MSX files.
WAVGLUE	Wave Glue: It's a tool to merge various sound .wav files into a single one. Even you can indicate to set a pause between them. Only supports wav files of the same sample rate, etc. and with only basic "chunks" or blocks inside wav files. Using this tool in conjunction with MSXF2W provides a way to create tape sound images of any game or program. (I've used this to create the wav images of my games)
HEXD and HEXC	Hexadecimal Decoder: It's a general purpose utility that allows you to see the contents of any file, in hexadecimal and ASCII chars. It0s useful to debug little machine code binary files. With the -s option, the utiliity shows only the hexa information without headers nor ASCII info. An example: HEXD LINE4.BIN -s > LINE4.TXT shows the hexadecimal code of each byte in the LINE4.BIN file, and redirects the output to create the LINE4.TXT file with the data. Hexadecimal enCoder: It's the reverse utility of HEXD. It creates a binary file from an original text with hexa codes, format provided by executing HEXD -s. An example: HEXC LINE4.TXT LINE.BIN will create a LINE.BIN binary file, and if you followed the example of HEXD, LINE.BIN and LINE4.BIN will be the same.

Other useful utilities are...

MSXTAPE	Msx Tape Loader: same as above but the original Linux files at Zoran Majcenic page.
TAPE2HDD	Msx Tape to Hard disk: It's a great utility to recover files from tapes and save as bin and ASCII files. It works on MS-DOS and the sound blaster, and has some improvements to get data even form bad quality tapes. I could recovered many of my best files by using it. It's a program from nocash , and you can have it also from its web.
MSXCas2Files   Regenerador	MSX Cassette to File: this is an utility to convert .wav files into .DSK ones, ready to play them from emulator. It's a program in spanish but I guess you will have no problem at all to see how it works. This version only supports wav files recorded at 22KHz. Also there is an utility to regenerate noised records, that you can apply to your wav files in order to get a cleaned one. There are two programs from Miguel Colom. In his web page you could find also an explanation of how works MSXCas2Files
DSKTOOL	Disk Tool: It's a good tool to manage disks files .DSK. You can binary, .BAS, etc. to any .DSK file that the MSX emulators will see as a disk. It's a tool from Ricardo Bittencourt, and you can find more information at his page.
AsMSX	Assembler MSX: It's an assembler for PC. There are still some bugs, but it was useful to compile Z80 instructions to code files. It's a program of Eduardo A. Robsy.