“Give me FIVE!" – A QRP SSB multiband transceiver by DK7IH
Building a multi band rig is, as you might conceive, much more complicated than setting up a monobander. Seems sensible.
https://dk7ih.de/2015/12/08/gimme-five-a-qrp-ssb-transceiver-for-5-bands-with-10-watts-output-power/

A multi-band SSB QRP TRX by DM3MAT
Inspired by a design by SP5AHT, I wanted to build a multi-band SSB rig as my first TRX design (a bit bold, I know). The SP5AHT design is a super-het using only two SA612 ICs.
https://dm3mat.darc.de/ssb2018/

A QRP SSB Transceiver by WB9IPA
After having been substantially inactive for the last several years, I decided to get back into amateur radio. Having always preferred tinkering with radios over operating them, I decided ... to build a radio ...
http://www.qsl.net/wb9ipa/Gen1.htm

An experimental DSB/CW QRP rig for 20 and 40 meter bands by IK3OIL
The building of an HF phone rig today isn't shurely a simple job, however I'd like to propose an easy-tomake project, suited for portable or emergency use.
http://www.ik3oil.it/_private/QRP%20sperimentale%20in%20DSB_eng.pdf

An experimental HF 6-band SSB transceiver by DK7IH
An SSB radio for the HF bands will be presented. Featuring 12 to 20 Watts of output power (depending on DC supply), full DDS frequency generation, covering 6 major frequency bands (1.8, 3.5, 7, 14, 21 and 28 MHz) within the short wave amateur radio spectrum. The rig also features colored LCD and front panel backlight.
https://dk7ih.de/2020/01/an-experimental-hf-6-band-ssb-transceiver-part-1-basic-outline/

DDS HF Transceiver SSB/CW by YO4HFU
This SSB/CW transceiver is designed to cover 160m-10m amateur bands. VU3CNS DDS with AD9850/1 was used with satisfactory performances. Some spurious can be found above 14MHz band. DDS clock signal (150MHz) is an external oscillator to minimize the phase noise.
https://www.qsl.net/yo4hfu/TCVR_HF_DDS.html

Direct Conversion HF Transceiver with DDS LO by OH7SV & OH2NLT
Direct conversion HF radio with DDS frequency synthesizer is very interesting concept. OH7SV and OH2NLT are experimenting with such rig. Full stories will become available when project matures. Here we have some preview pictures and material.
http://www.saunalahti.fi/hohtola/ham/DC-TRCVR/DCradio.htm

Four Band CW Transceiver by PA2OHH
The performance of the 80 meter CW transceiver using the phase method for side band suppression is very good. Construction was easy with all good obtainable standard electronic components ...
http://www.qsl.net/pa2ohh/99trx.htm

High Performance HF Transceiver by YO3DAC/VA3IUL
High Performance HF Transceiver.
http://www.qsl.net/va3iul/High_Performance_HF_Transceiver/high_performance_hf_transceiver.htm
 

Home brew HF SSB transceiver by VK3EPW
I responded a CQ call on 14.160MHz today and ended up having an entertaining conversation with Peter, VK3EPW. He's 1,000Km away, was running 15W and using a home made transceiver, so naturally I asked for more information.
http://blog.marxy.org/2008/12/home-brew-20m-ssb-transceiver-by-vk3epw.html

Home-Made KW-Transceiver durch DC4KU
Prinzipaufbau eines großsignalfesten KW-Transceivers mit hochliegender 1. ZF.
http://www.dc4ku.darc.de/KW_Transceiver.pdf
 

JUMA-TRX2 High Performance Transceiver by OH2NLT & OH7SV
JUMA TRX2A is a high dynamic range transceiver for SSB and CW, using the quadrature sampling technique for demodulation and modulation with the low noise phasing method.
http://www.jumaradio.com/juma-trx2/

Multiband shortwave tranceiver by PE1JPD
During the spring 2013 I decided to build a shortwave transceiver to participate in the vacation round on 40meters. First with 15W only on 40 meters, and with an open dipole on the camping 3 meters above ground I worked a lot of stations in all of Europe.
http://www.pe1jpd.nl/index.php/mutiband-shortwave-trx/

SPOTTO - A Direct Conversion High Performance Universal DSB Transceiver by KANG. K.P.S.
When I incepted the design of SPOTTO the focus was mainly on a simple and quieter high performance receiver with excellent sensitivity and dynamic performance combined with a simple DSB transmitter offering cleanest and moderate output for QRP use.
http://www.hamradio.in/circuits/spotto.php

The G4CLF Transceiver Board by G4CLF
The G4CLF Transceiver is the heart of a simple, but high performance, SSB transceiver system developed in the Applications Laboratories of Plessey Semiconductors Ltd in the late 1970s and published in 1980.
http://jbryant.eu/pages/g4clf.htm